This is a question I get multiple times a month. The simple answer, no deeper than 1/2 inch for daily maintenance. After all, as a groundskeeper, you are attempting to maintain the top 1/4-1/2 inch during the playing season. Please see the photo below. This photo was taken at Brandon Phillips Field in Cincinnati on Saturday. Using a quarter as a point of reference, this nail drag was pulled at a depth of 1/2 inch.
Look for additional posts on drags, conditioners, etc later this week.
Go to j-dturf.com to learn more about J&D Turf.