Jeff, One caveat, if the grass is taught to be thirsty,
many of these grass bunkers will remain softer than
normal areas. Most often they have drains at their bottoms.
Even with the drains, the bottom of the bunker often gets deep equiptment tracks, in addition to the grass being
extra lush. Other than that, I think their judicious use
is a great addition. Especially in key spots such as a
bail out alternative to sand. If the green's sections
are small and run away from this grass hollow,
the shot is actually more difficult than sand. IMO.
Pinon Hills uses them exquisitely.
while this schematic doesn't depict it very well.
Just to the left of the middle of the green
is a grass bunker that illustrates my above comments.