It's a great place to prove and improve your skills, while keeping your time investment worthwhile.
Hard to outline anything particular, I guess the very first development challenge comes to mind since it was rather impactful. It was a rather tough Assembly, and I barely made it before the deadline, but since the result wasn't too bad (2nd place) considering I was rather clueless about many challenge's aspects I decided to continue competing.
Fitness, Sports, Music, Anime, Video games
Don't expect everything to be easy and go smoothly, but your efforts will eventually pay off.
I was a Topcoder member since high school, back then I was into data science so I was competing in SRMs. After getting exam-free entry to university, data science seemed to pay off already, so I gradually lost interest.
After a while I received a newsletter about the TC Swift campaign. I was working as an iOS dev for a couple of years, so picking up Swift seemed a natural thing to do, hence I've decided to try competing in TC development challenges.