or, stoneskin an entire party for a fight, damage comes in, you don't have to focus as much on dps/other healer because you were clever enough to have a stoneskin on them, and now have possibly a gcd or two to focus on the tanks initial damage intake before looking at dealing with more damage on dps.

seriously. if you have a shield there, why not use it? what's the harm of that 3 seconds or so it takes to cast.