#1) Get a realistic budget. But, getting pre-approved gives you an idea of what you can afford, but ALSO what it will cost you on a monthly basis. When you get it down on paper, you may decide that you want to be well below your maximum approval amount. It is hard to think logically about that when you have fallen in love with a home that is above that limit.
#2) Credit reports are often incorrect. If you wait to find the house before you get a pre-approval, you may not know about the apartment complex that sent you to collections improperly. Or, the item that got put on your credit report by mistake. Nothing more frustrating than finding a house, knowing you can afford it, but not being able to get a credit issue resolved in time to buy it.
#3) Shopping completely out of your price range. It is one thing to fall in love with a home you qualify for, but is more than you want to spend per month. It is another altogether to find a home that is just out of your price range altogether and there is no way for you to buy the home. If you are looking in the 250k range, and then have to drop to 200k, you will have set yourself up to most likely be disappointed in the house that you eventually get. And, buying a home should be an exciting and happy time, not a time of begrudging settling.
#4) You may be able to afford more than you think. Interest rates are way low, and the cost of home ownership is lower than it has ever been. Not to mention that there are tons of programs for 100% or near 100% financing, or very low down payments. So, if you meet with a qualified mortgage specialist, you may find that you are able to buy more than you ever thought you could. This is not as rare as you would think.
#5) This is probably one of the biggest factors in the whole deal. We are in a seller's market. Sure, prices are still repressed and buyers can still get a good deal. However, there is the lowest inventory of homes we have seen in 12 years. From a months supply of inventory standpoint, this is the lowest inventory our area has ever seen historically since they began tracking the statistic. Seller's can be picky. If you don't have that piece of paper that takes 15 minutes to get, a seller will bypass your offer and go to the next one that is pre-approved. And, by the time you get notice that you are pre-approved and resubmit the offer, that home will have likely gone under contract. That is, if it is priced right and in good condition.
The bottom line is that 15 minutes is a small time investment. In the end, it will save you time, it will save you hassle, and it not getting it may prevent you from getting the exact home you have been looking for.