What does credit risk department do in banks?

In basic terms they are emplyed to check out customers applying for loans (credit) and identify those who are likely not to be (a) able to make replyments. (b)default on their loan agreement willfully i.e. take out a loan knowing that they are not intending repaying

(c) identify those customers who apply for a loan and who are already exceeding their ability to pay.

These are all risks to the banks money lending capability. The department will eith approve teh customer as safe (they can repay) or not safe and the loan or credit limits are revoked.