A/C compressor is broken?

I’m in the process of buying this Mercedes but the A/C compressor is broken. I get they say it needs to be replaced. They drive it every day no problems so they say and I’m just wondering how detrimental to the cars engine is it like is it just air conditioning that’s not going to work or what else is involved in it like what can happen to it and is it imperative that I get it replaced?