IIP is generally good as long as that doesn't make the loot absolutely worthless.
If you only get a weapon of anti liches after killing the only lich in the game that doesn't feel satisfying. But if you get it after killing a particularly hard one, and there will be more in the future, then the humor is felt but there is still a reward. Or if it is the only lich, the weapon should have other effects to make it worth it.
That being said, in general it is pretty great to have IIP.
