If a sealer is:
- Chosen correctly for the application goals
- Applied as directed
- Not need to be re-applied for a very long time, if ever.
- Not peel or discolor
- Save more money from the application labor cost than the sealer cost.
- "Breathe" (not trap moisture beneath the surface)
And can also (depending on sealer type):
- Enhance natural material colors
- Improve color defects in grout and/or surface material (solvent-penetrating type)
- On exteriors - eliminate freeze/thaw spalling (popping the surface) caused by exterior water entry (penetrating type)
- Stop efflorescence salts from migrating to the surface (penetrating type)
- Strengthen weak grout or surface material (solvent-penetrating type)
- Strengthen bond of grout to surfacing edge (solvent-penetrating type)
- Stop lime pops on Mexican Tile (solvent-penetrating type)
- Not change appearance at all (water-penetrating type)
And also -- look pretty!