It may not seem like it has a niche currently, but with Cataclysm still deep in development, they could make it so this might add some of the "Depth" to healing that designers are looking for. Otherwise, very few mobs and raid-level bosses have a substantial amount of resistance to overcome. For additional resistance due to level difference, spell penetration has no effect. For example, A level 70 player casts a fire spell at a level 73 raid boss with no innate resistance. You can help expand it by editing it. The level difference is 3, so the raid boss has effectively 15 resistance to all schools against the level 70 caster.
No matter how much spell penetration the caster has, his spell's resist check will always be done as if the target had 15 resistance.
No matter how much spell penetration the caster has, his spell's resist check will always be done as if the target had 15 resistance. What is it like to form a guild in WoW? It has been estimated that Rage Winterchill has approximately Frost Resistance and that Supremus has approximately Fire Resistance. Spell penetration cannot reduce a target's resistance below zero. How interesting would it be if Spell Penetration became somewhat useful for certain encounters in PvE? Here, the min function means the minimum of two values - in this case, it shows that spell penetration greater than a target's base resistance has no effect.