I've just done an archive and install to get my system back to where it needed to be (the sound stopped working) and I was wondering; now that I'm up and running perfectly, can I trash the 'previous systems' folder or is it required to operate now?
I'm no expert DrewNL, but I can tell you that I trashed and then emptied the trash, dumping the previous system folder many, many times after an archive and install. It is huge and I've never had an issue once the system is running to my satisfaction. It gains huge space on your HD as well.
The only thing that might possibly (repeat, possibly) be in your Previous System folder that you wouldn't want to trash are perhaps some specially-installed fonts (not a good idea, btw) or some System-level patches/alterations (again, not a good idea and more aimed at UNIX geeks than us "normal" people).