I especially agree with the easily reconfigurable air plenum. Our data center has a mixture of custom built cages and cabint rows, so hot/cold aisles are difficult to maintain. The raised floor lets me reconfigure based on where hot and cold spots develop depending on how our customers reconfigure their equipment and what time of year it is (we're in Texas). I walk through the data center with an IR gun every few months and rearrange the perferated tiles as needed.

Putting the cable racks under the floor keeps them out of sight so that you don't have to spend a lot of time dressing in new cables or learning to ignore ugly cable trays.