Age old question, indeed!
All of this depends on how much acutual climbing someone is able to do in addition to their hang boarding. If someone is able to do a lot of climbing then max hangs a couple times every 10-14 days will work just fine. If not, then hang boarding more often is prudent. The thing to remember is that climbing movement is the best way to apply any finger strength. So decoupling fingers away from what is done on the rock will only make it more difficult to bring that strength in the presence of full body movement when the time comes.