What is the best way to approve certain expense reports automatically

Good afternoon everyone,

I have a question regarding risk templates in Expense. I have a user that would like to see what the best way to approve certain types of expense reports automatically that are under a certain dollar amount. This will help him so that he doesn't have to spend time and resources on touching those expense reports. Also, What are some of the risks associated with that. For example, he would like to have all of the expense reports that are for mileage reimbursement under $250 to be approved automatically. He will then do random audits on some of those expense