I have only used them in the Paladin stronghold quest in BG2 and a few times as a paladin (killing everything that was evil - just looking for an excuse).
They are helpful to know whether some spells and effects will work on certain NPC's. I've not really used them before, but it would actually be helpful to know.
Know alignment can be useful if you forget your party members' alignment AND you forget which key opens up the character screen to look it up AND you don't check the wiki.
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Besides that I have never ever used the spells.
Yeah, that is what I assumed but I was hoping I was wrong.