ATF - the Rules of the Air apply to all pilots, both professional and private, and as such have to be pitched at the "dumbest" level (No offence meant to PPL(H)s.)to give a wide margin for safety. A bit like the red line on the airspeed indicator. We all know the aircraft will do much more than that without falling apart, but we respect that limitation anyway (I hope...)
When you apply for an exemption, you have to supply information to Charlie Alpha Alpha about how you will perform this task safely and without danger etc etc. And you have to be a "professional" pilot working on an AOC to get one. The idea is that the CAA trusts you (as a responsible, professional flier) to evaluate the risks involved and prove you can do the task without putting the aircraft or any people in danger.
I have an exemption to 200' on my filming sorties. This does not exempt me from the basic premise that I should fly the aircraft safely, and at all times be able to land the heli safely in the event of a power failure.
You say :
"Surely if its a filming job and everyone is consenting and made fully aware of the dangers then it shouldn't be an issue"
Tosh! It doesn't matter who consents, especially not film directors and camermen , who are notorious for wanting to get closer and lower no matter how close or low you are. At the end of the day, it is the pilot who will carry the can when the !!!!! hits the fan, as the camera crew are packing up their kit and slinking off, dramatic pictures safely in the can.
To take it to the extreme - "Well guys, yes I will hover my heli over your head at 20' as you ask so you can get some great pictures. However, if the engine stops and I crash on you, I can't be held responsible because you were aware of the dangers..."
So to answer your question, no an exemption doesn't make the helicopter fly any safer - in the same way that a radio licence doesn't make it fly any safer, but you need one of those anyway!