By looking at and comparing the actual numbers in the statblock, along with the various extra abilities.
If I'm running an NPC as a foe for the party I want and need to know what it can do, what it can't do, and what its numbers are; and the more detail I have on such things, the better.
What's it's class and level? Just knowing those tells me a lot about what it has going for it.
What languages does it speak? Is it likely to understand the party's shouted communications with each other during the fight? Never mind it's hard to monologue effectively if nobody in the party can understand me.
What spells does it have prepared? Also, what other spells does it have in its book? Inquiring minds are going to want to know.
And so on.