An example may be as such:

It takes 75,000 AA miles to book a certain award itinerary. You are a family of four so it will be 300,000 AA miles to do it. You call AA and ask them to put the flight on hold and they do so for five days. It is all set up based on your AA account for now. Maybe you were expecting some miles to post and needed more time before finally booking everything. But you only have say 75,000 miles in your account and those miles are slow to post, whereas your wife has the other 225,000 miles. You can now do it with two accounts. So when you call AA back, you can ask them to split it up such that they book one person with your miles and the rest of the family with your wifes miles. 300k used and everyone on the same itinerary.

MM