Like other posters have said, 10-12 hours is doable in a day, but we split it up simply to get more time at WDW (without using more vacation).
Why spend an evening at home when you could be putting miles behind you!!
Also, except for hubby's CPAP machine, we have duplicate toiletries, and wear totally different clothes for work than Disney, so can be packed days ahead!
I know it's different with young kids.
On a different vein, we leave the night before and head up to Ocala because we're not getting any younger, and arriving home at 2am, then going to work just doesn't make any sense for us any more.
We would fly more often, but our only direct flight has moved to terrible times and connecting in Atlanta takes almost as long as driving.