Comment by qbasic_forever

Banks and organizations that are considering lending you credit (i.e. buying a house / car / getting a credit card) can know if you're getting in over your head with finances and might be higher risk to repay. They can set their interest rates and fees appropriately.

Although all that said for any major loan the bank is going to ask you to provide detailed proof of all income, assets, etc. They likely use this service as a check to make sure you aren't trying to overstate your income.