In the embedded link there are 5 great reasons to have a pre approval and why your realtor wants you to have one in place.
I might add, that not all pre approvals are created equal. A top realtor in our area called me asking about a pre approval a client received from a different brokerage. Then when the client purchased the deal was declined. There are many reasons this can happen, but it shouldn't or not often.
A pre approval should require an in depth application collected, consent for credit to be pulled and reviewed. Income should be collected, down payment should be understood and if possible verified and the type of property should be considered. Even the difference in not considering a condo fee can kill a deal by not asking if the client is buying a detached home or condominium. We love pre approvals and we do them well.
Check out why your realtor loves them as well and let us do your next pre approval!