I've done a few restorations--I'm blanking on the proprietary name.
Generally I've used them for onlays instead of full crowns where I think
the patient has a problem with wear from grinding and clenching.  They
are softer than porcelain which will lessen damage from parafunction.
But because they are softer, they will wear more quickly themselves.
And now there are lower index porcelains that don't wear opposing teeth
as much.  I don't really find much use for them overall.

Steve