Most natural stone that is porous enough to absorb water or oil born stains benefits from a protective sealer.
The reason for using sealers is to prevent staining as well as prevent damage and loosing the stones bond to it's substrate from freeze and thaw.
Common household foods may stain many natural stones if not protected with a good impregnating sealer.
Sealers can be invisible, as to not change the color of the stone and there are color enhancing sealers that bring out the color of the stone. Also there are topical sealers that can give a satin to a high gloss look.
All these sealers will help protect from staining of natural stone.
Good impregnating sealers will breath allowing water vapor transmission from the stone. Topical sealers generally do not allow moisture with in the stone to escape, there for, topical sealer coatings should be limited to areas not prone to excessive water.
Most sealers called "impregnating sealers" have a carrier that delivers the protective molecules into the stone and do not change the stone's appearance.
These sealers have water, alcohol, or petroleum based products as a carrier to deliver the water/oil resistant sealer into the stones surface.
Some sealers have a warranty that is given by an 'accredited applicator' or just the product itself.
The main reason to seal natural stone is to make cleaning easier and to prevent stains. Otherwise!………….Don't Seal your Stone.