Lowbie instance farming with Holy Nova (use the trinket, since it procs off any damage hit, even a 1 damage hit will proc it).
Jin'do the Hexxer in Zul'Gurub - Use it when you have a lot of shades attacking you. Since they do 1 damage, you'll be gaining 34 life every time you are hit.
PvP - Save yourself from a untimely death in case that warrior charges you. 500 may not be a lot, but for a priest with Inner Fire active it can up your armor to 2000, which is a similar amount of mitigation to a rogue, if not more.
While activated this trinket uses a graphic identical to that of Blessing of Protection, when used in PvP, this may stop or throw your enemy off balance thinking you are immune to physical damage.