Not having protection from good is unhelpful against paladins etc.

However, if you are uncaballed, say, and can chose your fights, there's a lot to be said for having protection from evil as an ap, for example.

Why? Because evil dudes tend not to have as many healing options as good aligned guys. And they also won't have protection against you (as in, they won't have protection from evil).

So evil guys will be at a disadvantage against you. I've seriously considered this route in the past when I found an ap I was playing seemed to be preying on Empire more than all the other cabals put together.