Unless you have hundreds of thousands of dollars in the bank ready to spend on a home, you're going to need a mortgage. So do you need to get pre-approved or pre-qualified for a mortgage?
Well, before you begin making offers on any homes you want to purchase, you need to speak with a lender. There, you will be able to pre-qualify for a loan right away based on the information you disclose (often verbally) about your financial situation. This will give you an idea of the dollar amount you are able to spend on a house and how much your monthly mortgage payments will be.
Pre-approval is different. After your lender receives the documentation needed to solidify your ability to pay a mortgage and everything has been looked over by an underwriter, you will receive a pre-approval letter.
Sellers will more seriously consider an offer with a solid pre-approval letter included. This indicates that the buyer's financing is ready to go and contingent only upon the appraisal of the home. It's about as close to being a cash buyer as you can be - reliable and clean.