It is often only one though if the ball is being returned to the side that was in possession as is the etiquette* for stappages for injuries.
* unless you are Arsenal.
I thought it was only goal kicks that dictate that the ball muct leave the penalty area. If it is a free kick then surely the same rules apply as everywhere else on the pitch. minimum distance the ball must travel (unless it has to visibly roll one revolution - like that awful Arsenal penalty...