I understand that big-big isn't something to use on a regular basis. I once tore up my DA rear dérailleur when my bike fell over to the right and I didn't check the hanger, then shifted the RD into the spokes. I see more chance for problems shifting to the small ring under pressure in a race than going to big-big...but then I'm pretty careful to check that hangar since that disaster. On a long hill, I'll shift to the small ring early on.