If your final cut pro library is taking up hard drive space, filling up your hard drive, AND if you're using an M1 or M2 mac, I can fix it!
Video Editing Tips.
First go up to file, then Delete Generated clip files, check all the boxes, this WILL NOT affect your project at all. That gets rid of bloated temp files, THEN
go up to Final Cut Pro menu, go to settings, choose playback and deselect background render. Your M1 or better processor can actually handle rendering everything in real time - when that box is checked, the computer is basically rendering a finished version of your project every time you change any little thing so that it will playback smoother on older macs. But for some reason it keeps those files and fills up your hard drive!