When I have a next action that I can do on a specific day, like an errand that has been on my next action list (@Errands), I will go into the Task and add the date that I am going to be in that particular area of town or wherever. So I do use Tasks on the calendar for needs like this. It doesn't HAVE to be done on that day, but it's nice looking at my calendar on my Palm and seeing the Task there to remind me that I can do it on that day.
Also, I do set up monthly reminders as "floating events" in the calendar (Datebook feature). For instance, I set a contact every 8 weeks for my customers, so I'll put a floating reminder at the beginning of that particular week on the calendar. It doesn't necessarily have to be done on that day, but I know I have to get it done that week.
Not sure if this is exactly what you are referring to, but just my thoughts.