It probably backs up your [R]eal [T]ime aves, though each RTS file is 4 MB each so you need to know if you have enough space. You can only set it for each game anyways. I think what it does is create another realtime save file with a different name/end to it with like a number 2 or something. That's what I think it does anyways.
Just tried it, it generated "RTS File 1" and "RTS File 2", so all it does is copy whatever RTS file 1 is into 2 so you can keep using 1 and if you screw up in your RTS file 1, you can load up your back up, RTS file 2.