I've not seen a decent computer room or DC without raised flooring.

It gives you a simple & easy route for cabling (via suitable holes in the floor tile under each cab. Generally 19" racks seem to be built for cable entry from the bottom, although I guess you could run cables from the side or top.

Not sure about this... but potentially the under floor void could be useful as an intake of cooler air.

If you've ever had to route bunches of cables beween cabs that are floor mounted you'll soon wish they had a big hole in the floor to an accessible under floor void :-)