Well, everyday cargo space is one reason. Keeping a spare, jack, first aid kit, emergency kit w/ blankets, water, non-perishable food in an out of the way space would be nice. That would allow us to keep a stroller in the back and still have room for groceries/hockey gear/etc.

The other reason is I'd like to have the spare and jack securely fastened to the car. Those could be deadly projectiles in a crash.

Plus I'm a big dude, my wife is tall and both our kids are tall, so I don't see the third row being terribly useful unless we suddenly befriend a pair of little people who also happen to lack their own transportation. I really don't see how anyone fits in those seats without some serious finesse.