There is an advantage in having both installed in that you can use one to do a screen capture to show a problem . or tutorial image in the other. I have PSP 8,X2, X3 and X4 all installed on the same computer. Hard disk memory is a minimal worry nowdays. And sometimes something works better in an earlier version of the program and as well some tutorials on the net use an earlier version and it is helpful to see how it works there first and follow the tutorial in that earlier version.