Reasons to get pre-approved, not just pre-qualified:

With pre-approval, you can determine which loan program best fits your needs and which incentive programs you might qualify for.

You will know exactly how much money you can borrow.  It's no fun to find your ideal home and then have your banker tell you that you can't afford it.

Your interest rate will be guaranteed for a period of time, usually 90 days.  This will protect you in case the interest rates start to rise.  You will know ahead of time, what your approximate monthly payment will be, allowing you to make a budget that is appropriate for your situation.

You will know what the down payment requirements are and what the closing costs will be.

And finally and this is the most important reason:  When it comes time to present your "Offer to Purchase" to the vendor, we are able to negotiate for you from a much stronger position.  A vendor always wants to be assured that they're not accepting an offer from an unqualified buyer.