You can do basic editing and format conversion. Without the Pro license, QuickTime is just a player. QuickTime Pro is actually an editor (play and write). You can even record external video with QT Pro. I have a license, but I also do a lot of video editing so it's sort of a necessity (besides it comes with FCP). Personally I think it's a little cheap of Apple to still be including a crippled version of QuickTime with OS X.
There are many other features as well.
However if you do only require the Full Screen, google for some freeware apps, like this one, and they work just as well. I'm not sure which one I'm using at the moment though