Performance mode is the nectar of the the Gods my man
While performance mode is generally most useful for live performances (thus the name), I would use it if all I did was noodle at home.
Performance mode is a method of putting your rigs into an organized set of banks. When in performance mode, the bank name is the name of the performance on the screen (you name them yourself). Each rig placed into a performance becomes a new rig. Any changes you make to that slot in the performance will only effect that performance slot (not anywhere else you use that rig).
An example of my usage is as follows:
For a given song (or type of song), I put clean rigs on the left and heavy rigs on the right. Every performance I have is setup this way so I can be assured that the far left rig will be a clean one and the far right rig will be a heavy one.
I also use performances to put the same rig into many slots, and then tweak the rig in each slot and A/B them to each other to see which one sounds best for a given usage. After I have the "golden" slot, I copy it and paste it into a real performance.
Performances are also useful for doing multiple sounds within a single song. For a song like "Kryptonite", you might have a nice clean on one slot, a crunch on the second slot, then a lead tone on the 3rd slot. You could name the performance "Kryptonite" and know exactly what you had in that set of rigs.