I fully agree with Alex above. Most of the time, the term is used for advertising, and the sealants applied by dealers, DiamondBrite, SupaGard etc, are useless and will come off with one good polish.

If you're talking about firms that use the term, and carry out a full treatment for your car where they apply a tinted resin - then that's up to the owner. I'd never let any process like that near any of my cars though

Gareth