Hello, one advantage of driving the entire head is you can lock the spindle in it's uppermost travel. That may reduce spindle run out/flex due to the reduced overhang on the bearings. Just as with milling on a conventional knee mill, I will move the knee instead of the quill.
Another less important advantage is the concealment of the driving parts verses having them hung off the front of the head.
Bubba pointed out the advantages to driving the spindle down feed. There are tradeoffs to both. JRouche
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)