If you're so low on space that 2-3 GB makes a difference, you're going to have serious problems with Photoshop in any case. It needs a lot more free space than that, anywhere from 100 GB to 1 TB, depending on file sizes, number of history states and number of open files.
You can also get general system problems. Worst case, it can freeze completely. You should never allow a system drive to fill up more than 60-70 %.
The beta version will continue introducing new features and new ways of using older features so the beta testers can look for bugs before the released version is released. I wouldn't use it for production, but I do use it for testing and some smaller projects.