For the report writer I built I have date fields that I then pass through strtotime which allows a lot of flexibility in how the date is formatted. And since I don't resolve the date until the report is ran it also allows for the use of relative dates (i.e.: yesterday, today, monday this week, etc).
Well we are now adding in a job that runs at the end of the work day, so I wanted a report that would get the results from that job but it wouldn't be ran until the next day. So a date range of "yesterday" - "yesterday" works except on Mondays when you'd want to go back to Friday's job and get it. Found the answer: "last weekday" - "yesterday". Fucking love that function. Adds so much flexibility with no additional work on my part.