Should I not use multiple jails?
I have small applications that don't require many resources in multiple jails.
Should I just move them over to a big jail? Would that free up resources or does it not matter much?
That's up to you. I have a number of jails, but they're set up with similar things combined in one jail. So Sonarr/Radarr/NZB/Transmission are one jail, Plex is another, etc. There isn't a great deal of overhead involved in running a jail.