New drywall, skimmed walls, you name it - pretty much any porous surface. Besides excellent adhesion, it makes it easy to get consistent gloss and sheen with fewer top coats in those difficult situations. Eggshell on a smooth wall or ceiling with grazing light come to mind, since I once had to 5 coat a new ceiling to get it perfect.Gardz is pretty good stuff, it's basically made to seal drywall where the paper facing has been removed. Only problem is it's clear.
I know SW and BM both have 0 voc primers.