Sellers typically will not accept an offer without proof that you can afford the house, and are approved for financing.
A pre-qualification is simply an ESTIMATE by a lender of what you can afford. A pre-approval is a more detailed process in which the lender investigates your credit history, and performs an extensive financial analysis to determine your ability to get a mortgage.
Getting a pre-approval is a safeguard to prevent the deal from falling apart due to failure to obtain financing. It is important to compare loans from several lenders to see which one is best for you. Once there is an inquiry on your credit report for mortgage approval, you have 30 days to seek out as many lenders as you want without it affecting your credit.
Schedule a free mortgage approval consultation here