In selection of a sealer you should make sure it would not alter the appearance of the product to which it is applied. It would be quite helpful to know what the intended floor care plan is. Occasionally you may encounter a situation where the intention is to apply a topical coating over an unglazed floor. In that case the sealer should either be part of the system or avoided. Penetrating sealers are relatively long lasting and difficult to remove. They will inhibit any attempt to bond a protective finish coat. If you are unsure of the floor care plan or are trying to prevent grout from bonding to a pitted glazed surface, such as those popular in many of the stone looks, a temporary grout release may be appropriate in that instance. Most manufactures of both grout and tile have specific recommendations. None of this is to say sealers are necessary, however, they can provide a fail-safe way to avoid film and staining.