Hello!

Without maintenance you will still get patches for the current version, but you won't get the interim patches that are made to address some problems immediately (EEF for expedited engineering fixes). Basically you pay to get these fixes faster, but they are not fully tested. For 7, 7.5 and 8 most of the EEFs behaved nicely for me and solved some issues. I remember that I had to uninstall one of them because it caused more issues that it solved. Overall it was worth it to me.

Premium maintenance means that you'll pay a premium for additional high priority access to help. This is basically only for professionals and studios who rely on the software for their business. 

Ciao
TD