Tile floors develop traffic patterns in the grout joints, similar to pathways on a carpet. Once the floor has been cleaned and rinsed, a clear, penetrating sealer is applied to protect grout joints from future discoloration without changing the appearance. This also extends the life of the grout.
Did you just purchase a home that was previously lived in? You will probably clean the oven, refrigerator, carpets and apply a fresh coat of paint, but what about the germs that are harboring in the grout lines, or on the tiles in your shower? Is there existing mold and mildew or soap-film?
New Homeowners who have just purchased their home, should consider cleaning and re-grouting their tubs & shower walls, coloring and sealing floor grout.