When should WHM use Stoneskin I?

[Saseal]

I just do,
-beginning of dungeon
-start casting just before the last monster is dead (sometimes I just forget or get lazy and just swiftcase SS II as we're all running off. It's not often I need SC for Raise when traversing trash mobs in dungeons)
-Before a boss pull
-After boss pull
-If I'm wary of spike damage on the tank
-SS myself (when I'm not frantic healing) if I find myself having a bad dodgey day

-and sometimes I'll just SC a SS II before everyone leaves the dungeon, to give some buffs for the road, if I liked the party. lol

Unfortunately, you're stuck SSing one at a time till you hit SSII. You can use Presence of Mind to speed it up if you really wanted to, at that stage, since you might not have Holy yet.

There was mention of SC for Holy - the only times I ever SC a Holy is for defensive use to stun things when shit is hitting fans (such as mid-spawning trash mobs in raids that tanks haven't picked up. I'll do it to stun trash thats on me, my co-healer or if I can identify the alliance member being hit is a squishy so they're not killed/extend time for peeps to get to killing the ADD(s)) or if theres just too much mob on the tank and need a few second breather to catch up (Bene + SC + Holy + Catch up).
But that's just me o_o