Do you think that investing time in personal side projects is a good way to advance your career faster, or could that time and energy be spent in a better way? Did you have a project that significantly pushed your career forward and in what ways did it contribute to you? You can describe what the project was about, how much time it took, and a link if it is public.
Yes, I do think it's a good way, at least for intermediate technical roles. The amount I learned building a side project was staggering. I felt so invested in getting to good solutions and had so little technical debt fettering me that I learned 24/7. My knowledge grew more with this project than it did in college + three years of post-college work.
I built Streamus (https://github.com/MeoMix/StreamusChromeExtension). It was a Google Chrome Extension that turned YouTube into a tab-free music player/playlister. It grew to 300k MAU by advertising organically through Reddit (https://www.reddit.com/r/Music/comments/2sypcn/seven_months_...)
I ended up becoming part of the Backbone Marionette organization on GitHub (they were the frontend framework I used to build it prior to React existing), I learned how to write, manage, and scale a full-stack application, and being able to cite the success of this project kept doors wide open for me when applying to future employers.
My next job after Streamus was joining a remote, profitable, bootstrapped startup with a team of ~40 people, had equity the company, and the company sold for 9 figures half a decade later.
A++, would do again in a heartbeat, no regrets - even though the project itself was shut down by YouTube's lawyers once it grew popular enough.
My personal side projects have helped me land jobs multiple times in the past, but they are absolutely not the way to advance your career.
Let me be very clear: career advancement and competency are entirely unrelated.
If you want to advance your career get a masters degree. Get promoted out of development as early as possible and learn to manage people, assets, and finances. You can be absolutely horrible with both software and dealing with people and still advance into more money and responsibility in the software industry.
If you want to be a better software developer spend lots of time writing original software progressively solving harder and harder problems. Odds are, I mean this absolutely overwhelmingly, you will have to do this entirely outside of work. Becoming brilliant in software is the equivalent of being a mindless patent clerk and toying with ideas about physics at night. You won't get hired for being brilliant until you make something brilliant. Sometimes that means asking for help. Consider that Einstein needed help with advanced math.
Why is this the case? Because the economics of software is not well understood and there is no established baseline of competence. The industry cannot even figure out how to tell competent developers apart from people who simply most enjoy hearing the sound of their voice.