I have never really understood filing VFR while in the military.
Nor have I, but that's the beauty of the flight schedule acting as a flight plan for the majority of the flights conducted as a rotorhead. The ODO has better vis than anybody. When we go on the road, we're still calling the ODO at the beginning and end of each leg, with the proposed route of flight, so once again - he's got better vis than anybody.
That said, while filing (and closing out!) when you're on the road is a royal PITA, especially when you're in a time crunch, I think the benefit of filing (aside from the fact that it's mandated by 3710) is that they people who call the ODO when you're overdue are the ones with the appropriate SAR assets on speed-dial. We've all stood some sort of ODO/SDO/FDO/whatever your command calls it, typically no more than a handful of times per month (and usually referencing procedures that are outdated by years!) Think of how much of a pain it is to try and find the number of the squadron next door when somebody calls for it...and then think of how much of a pain it would be to try to activate SAR assets for your overdue bird that is somewhere between, say, St. Louis and Milwaukee. Who would you call to activate a SAR plan? How would you get in contact with those agencies? What if your overdue aircraft is simply due to a boneheaded crew who arrived safely, gassed, and took off to another destination without calling you first?
Yes, the system sucks...but if the dookie hits the fan, I'd rather have FSS looking for me and initiating a SAR plan than rely on 1stLt Schmuckatelli (who, through no fault of his own doesn't know a damn thing about squadron flight operations and is stuck standing weekend SDO because he just checked in the week prior) screwing around trying to figure out what to do if he doesn't get a SOD call.