I restarted my Mac the other day and my free disk space went from 4GB to 40GB. Things are also noticeably zippier soon after a restart. Annoyingly, I can't reboot often because I'd lose all my incognito tabs. It's possible that quitting all applications would have the same effect (except the swap space, which seems not to fully release until reboot), but it's just as much hassle to do that as to fully restart the machine.