It means to look at the result of your decision in the past. This way, maybe, you can make a better decision now.

edit: I think Yisroel is correct. It sounds like "it" would refer to a person or animal that got something for the person being talked to in this sentence. (The word "it" is not commonly used to refer to people) For example if your dog brings something to you. I could tell you "Look what it got you." It is similar to the sentence "Look what he got you"

it means to tell you how good or bad something / someone is ex: 1) You went out with him before and look what it got you/ look how it went. 2) Before you cheat on the test look what it got you last time and ask yourself if it was worth it.