We have buyers tell us all the time they want to see a property but they are not pre-approved yet. They haven't even been pre-qualified (a quick check with a lender to estimate what a buyer can afford).
Currently we are in a seller's market. This means there are more buyers than there are houses available. There are certain price points that are getting contracts on the same day they are listed. Pre-approval is such a vital step and should happen before looking at properties, especially in a seller's market. It shows that you are a serious buyer. But there are other reasons to get pre-approval.
First, some listings require pre-approval before a buyer can even see the property. This is especially true in higher price points. Second, and related to the first point, pre-approval allows you as a buyer to not spend time looking at houses you can not afford. Third, when it comes time to make an offer, most listings require proof of pre-approval along with the contract. Finally, in a seller's market including pre-approval with the offer, even when it isn't required, makes the offer even stronger. The seller doesn't have to worry about a deal falling through because of lack of financing.