I have granite surfaces and within days of having it installed my son left a bottle of olive oil on the surface and it left a lovely oil mark
We called the company and they came and removed it by 'painting' some liquid in with a paintbrush. It took a few applications but it came out. They said I must treat it with a sealer once a year to stop stains like oil/red wine getting into the pores.
I have white granite and apparently it is much more porous than the darker ones. So really its not going to clean the granite and in fact the granite must be spotless otherwise treating it will cause any existing stains to become permanent.
I find when mine has just been treated it is much easier to wipe down and keep clean, just like after polishing a wooden floor its easier to mop.
I bought the stuff from the granite company, about £30 I think it was. Its easy to do yourself but takes a while and you cant use the surfaces for 24 hours.