Well, for one thing, Mom has a chance to run errands or take a nap without being interrupted (assuming there are no younger siblings). On the other hand, there are those that suggest that for our children's (particularly our sons') best intellectual, physical and social development, they should stay home and play with Mom as long as possible.
Newsweek: "Why Are School-Aged Boys Struggling?"
WSJ: "Protect Our Kids From Preschool"
I generally think the anti-intellectual kindergarten movement is one that doesn't necessarily apply to gifted kids--like the milestones lists don't apply--but I just thought I'd throw it out there...