I have never used SR and it's been always disabled on my system. If you are good with computers/Windows, disable it. If you are not, i think you should leave it on. I mean (most) problems can be fixed without using SR.
Not sure about the performance thing, but i guess that disabling it frees up some system recources. Also frees up some disk space. I have also read, that SR is not so good, cause it can store viruses as well.