Multiple mortgage applications

This topic has been touched upon in a few discussions over the years, but I have not found a clear/comprehensive response (ideally from someone who has gone through the process, or has experience in the industry) - basically, even though mortgage availability increased substantially, and apparaisals are coming in at the mark most of the time, there are risks. E.g. one gets pre-approved at several banks, but pre-approval is not a guarantee. What if they go with one bank that ends up not giving the loan? Or appraisal comes in well below the purchase price? Or the process takes forever and interest lock up expires? Etc etc. Does it make sense to fill in an application with two or three banks to hedge these risks? Has anyone on the board done that? What is the downside?