Pre-approval means your lender has looked in detail at your finances and certified that you would qualify for a certain loan amount. Below are some real advantages of getting pre-approved as you continue looking at homes:
Instead of the rough ballpark figures you've been working with, you now know how much money a lender will loan you for your new home. You'll know you're not wasting time on homes you can't afford.
You're in a stronger negotiating position when dealing with sellers, because they know there's far less chance of a financing issue causing problems. They'll find your offers more attractive, because you can back them up.
Mortgage approval can take time, especially if you need to assemble documentation or clear up questions for your lender. It's a good idea to start the process early so you can be ready when your offer is accepted and you're ready to close on a home. Nobody likes to put off a closing date or delay their move-in because of loan details.