A sealer is a liquid that soaks into the pores of the stone. It slows down how fast spills are absorbed, which buys you time to wipe them up. It does nothing about acid, because the surface is still bare stone.
A protection film is a thin physical layer on top of the stone. Spills and acids land on the film, not the stone, so it prevents both staining and etching.
If your stone is quartzite or granite, etching is not usually a concern and sealing may be all you need. If it is marble, limestone or travertine and it is in a kitchen, sealer alone will not keep it looking new.

