It does if you want to operate your self-flying taxi in an economically sound manner. All the time that it is on the ground it is not making money. Which means you'll be charging it when the number of requested rides is low, so you'll need to make a number (possibly quite a large number) of 15 minute rides before you get to recharge.

15 minute flight, 15 minute back to depot, 5 minute battery swap, charge batteries at the depot.