BigBoss recently posted an update on that states what the new 2.21 Categories updated.

I updated Categories to 2.21. The only change is that the backgrounder app is now optional so that those of you that didn’t like having this app could uninstall it without uninstalling categories as well. Of course, if you uninstall it, the backgrounding option inside categories will be ignored.

It is definitely a good thing to not have to be forced to install an app when you don’t want it, so good job BB smart move! As always keep those updates a comin’!