It can be a great boon proving you know when to use it. Here are some scenarios I utilize Stoneskin.

-When Titan/Ifrit Jumps
-When Garuda is traveling to you after warping
-Casting on yourself and the other tank when switching during Turn 2 of Coil
-Off Tank throwing it up on everyone after the wyverns in Turn 5 of Coil, making the first Fireball more sustainable.
-MT/OT throwing it up right before Twintania uses Death Sentence.