Go to any tech blog or forum and you'll see them sprinkled around everywhere. "My little side project", "been working on something like X for a bit", "this reminds me of a small tool I built for myself once". These might be software projects or some craft projects or some statistical analysis, but they're all fundamentally about the same thing: doing industry-related tasks that aren't tied to work.
The messaging from these posts and comments is pretty clear, and leads to more and more people trying to take up side projects on their own: if you're not working in your industry outside of your normal working hours, you're falling behind. You start to feel like the exception, like you'll never be able to keep up with these incredibly motivated people. I'm here to tell you that is 100% incorrect.
Benefits of side projects
I've dabbled in some personal software projects on the side from time to time. My dotfiles take up a lot of time outside of work, and I've built a tool to generate a weekly fantasy baseball summary for the league I play in. I've played around with some other projects, as well, but none of those ever held my attention for very long.
There are some real benefits to doing work in your industry outside of normal working hours. More practice is generally good, and especially when you're starting out, getting as much exposure as possible is the name of the game.
New tools and technologies
These have all be incredibly useful in their own ways. I treat these personal projects as ways to learn new programming languages and technologies. I briefly played around with a service-based version of my fantasy league report generator and got to learn Kotlin, gRPC, and Spring Boot. It was a great experience, but not one I ever pushed from my local repository. It didn't fit the purpose of the published project.
I'm currently learning Rust and test-driven development by building a pre-commit clone (I've had a couple brief posts on this already), and I've spent a good amount of time recently playing around with Neovim and Emacs to make sure I'm not missing out on any killer features from other text editors.
New careers
Of course, others view these side projects as a path to a new job or position. Sometimes the requirements for moving up the ladder just aren't available during the workday. If you want to get to a senior software engineering position at your company but you currently run user and regression testing, you likely won't have the time to practice your coding skills on the job.
Others view it as a way to kickstart a new company idea. Working 4 hours a night on a side project may seem like a lot, but every once in a while you'll hear about someone who came out of the process with a whole new company. I personally don't know anyone who has made that work, but I have heard of side projects that have been viewed very favorably during interview processes.
Better skills
I was a terrible developer until I started reading books on coding best practices. Once I discovered that there could be better and worse versions of the same code, I took it upon myself to rewrite some of the previous things I'd done in a better, more maintainable way. Some of these things were done on projects outside of work, but many were refactorings of some previous things I'd done at work.
I doubt people liked reading through those pull requests, but they were instrumental in making me understand how to read, write, and think about code.
Finding the balance
With all those great points in favor of side projects, you may think that I'm advocating for you to start picking them up. This is not true. There are real downsides to working hard on a side project, both mental and physical.
Time
The most valuable thing you have available to you is your time. It's non-replenishable and always in short supply. Side projects eat quite a bit of time.
If you have the "normal" American work hours, you'll spend 8 hours a day at work, 2 hours commuting and 7 or 8 hours sleeping. You may spend 2 hours cooking and eating, and probably need an hour to handle other things like showering, cleaning, and doing laundry. That's at least 20 hours a day that's pre-allocated for you.
In those remaining 3-4 hours, you have a chance to be yourself. You could exercise, hang out with friends, play games, read a book. Basically, those hours are where you build your personality and your hobbies.
If you want your identity to be the one that's always working, you can keep working on those side projects. But if you don't want to be that person and instead want to be the person who knows about the latest TV shows or is dedicated to a sports team, you'll find it hard to find the time to work on anything on the side.
A good compromise might be to only work on your side project before your day job. For most people (certainly myself), that seriously limits the number of hours I can work on the thing, while also using my most creative time of the day to do something new. My peak focus hours, on the other hand, tend to still fall during my normal work hours, and so I don't see a dip in productivity at work.
Or, you might decide to only think about your side project on the weekends. Or 3 times a week. Or only for half an hour a day. There are plenty of ways to make it manageable, but most of the people I know tend to work on their projects late into the night, cutting into sleep that's badly needed.
Burnout
Sometimes you find the time and the motivation to keep working after you've left work for the day, like I did when I discovered that I had been writing terrible code. You may then run into the problem of burnout.
Burnout has been getting a lot of press recently, and for good reason. I've suffered from burnout, as have many of my friends, and I can tell you that it doesn't just get better. My instinct was to try to work harder; things weren't feeling right at work, and I assumed that it was because I wasn't at the right level. So I doubled down, hoping that by working more and working harder, I could produce more at work and stop feeling like things weren't going well.
Side projects can sometimes bring the stresses of work home. Not everyone can think about writing code for 10 hours a day. Not everyone can do carpentry in the spare time. Most of us need time to do something else before we can be efficient at our jobs again.
And while you might think that you're building the side project that will set you free from that job, the job is also the thing that's (currently) guaranteed to pay you. Side projects and new companies can take a long time to get going and pay out. You won't be generating $1 million in revenue in your first year turning your project into a company unless you struct metaphorical gold. You'll be doing the same type of thing you were doing for quite a while, just without the guaranteed paycheck.
There is no good solution to burnout. You can only monitor that for yourself, and, as I've experienced, your reaction to it may be to double down and try to work even harder. If you find that you're enjoying your job less, or feel like your performance there is suffering, it may be time to evaluate the resources you're pouring into your side projects.