Concrete sealer and stain fulfill two main purposes: supporting the strength of the concrete and providing a protective coat.
There is a broad range of different products available on the market, some concrete hardeners are even mixed into the cement paste before it is poured. However, only sealants, stain or paint add a protective coating to the surface.
This layer prevents spilled liquids or water from soaking into the concrete and increases the water-resistance and general resilience of your concrete surface. Otherwise, even accidentally spilled red wine, for instance, could require a re-sanding of the entire surface to restore its perfect look.