Casting Stoneskin doesn't pull anywhere near the same amount of hate as casting Regen, so I can understand switching to spamming Stoneskin rather than Cure if you're pulling ahead in the hate table for some reason.

Whilst levelling PLD up, I've tended to throw a Stoneskin on myself after each group of mobs unless there's a WHM in the group (their SS is more powerful due to traits, but mine's the same as a SCH)
I'll sometimes use it on myself mid-fight if I've got plenty of hate as an extra mitigation cooldown, particularly whenever the mob is pausing to cast an AoE/Cone and I've already sidestepped out of the way - less chance of being interrupted.