At my airline, there has to be at least one FD crew member present for passenger boarding to commence (plus the full complement of CC).....and the VHF radios must be continuosly monitored while the a/c is on the ground with pax or crew on board..............and we jolly well like it like that!
......cos we dont have to worry about the Cabin crew learning to operate the radios if there are no FD crew present.
We also have the option, SCD, to have the headcount done after the doors are closed. This is usually for delay reporting and pushback truck / start up clearance sequencing, and is more relevant at some airfields than others, depending on whether we are on an airbridge or on the ramp, etc. It is particularly useful at our very busy home base where the pushback truck will not even attach until the doors are closed and beacon on.
Have to say though that the number of occassions that the headcount and loadsheet figures do not tally is relatively very small......maybe we are just very lucky to have very good handling agents
so it works for us.