I learned regex in a data entry job when receiving spreadsheets of user info they entered themselves. The number of times I went from a 40-minute by-hand solution to a 30-second one was astounding.
Need to clean up capitalization? Regex.
Need to fix all the phone numbers with dashes in them? Regex.
Need to make sure all the emails are valid? Regex.
So many hours of tedium saved. It really is one of the most powerful tools to have in your back pocket.