It also depends who you are playing. For example, Michigan State rarely gives up offensive rebounds and will run when they get the board you probably send everyone/almost everyone back. If you are playing Wisconsin who rarely runs, you can probably crash the offensive boards and only send one or two back.
This year they didn't crash the boards much because they didn't have guys who were good offensive rebounders and it made more sense to prevent the break than to hope that 3% chance of getting the offensive board worked.