Sometimes it pays to re-vist old work, and revamp it. Other times, it’s best to just scrap everything that you’ve done and start from scratch.
I’ve gotten the fun/pleasure of doing the latter, and am working through an old(ish) fantasy world and giving it a complete overhaul after realizing that the initial story line and plot was… not good. Which is good! I’m getting better and better at finding what does and does not work for myself, and getting to the point where it’s easier for me to tell what’s good material and what isn’t.