Calling day by day is only necessary for certain types of units at some times of the year. Other wise, you can just make one call to get your first choice.
For example, if you want either a guaranteed Boardwalk view or a standard view room at the BWV anytime in November or December (and probably October), you'd better call day by day as soon as MS opens. I call day by day for a standard view in early December - it's the only way to get what I want without having to suffer through the uncertainty of the waitlist. Many here will also recommend you call day by day if you want a Grand Villa anywhere (including VB). Those are very popular and often book early, especially the lower point villas at OKW.
Since the competition to get into one of the smaller resorts at the 7 month window is increasing every day, many recommend calling day by day as soon as the 7 month window opens if you want something at BCV, VWL or BWV.
If you aren't sure, call MS for your first day and ask the CM for advice. They have a pretty good idea of how quickly things are booking and will tell you if you need to continue calling day by day or if you can safely wait and only make one more call.
Best wishes -