Radalt the point is the course that you are on at the detached unit is for the services benefit, the service has sent you on the course and just as it pays for your travel and accomodation at a hotel if no service accom is available it should also pay for your food.
Imagine a young LAC married with three children in the run up to xmas or the month after xmas ( even worse ) his missus has spent all the months remaining money on food, his cupboards are full, he then gets sent on a two week course short notice cos someone else pulls out! he is then expected to pay for his food through no choice of his own!!
If you are happy with the erosion of morale sapping rules like this then good luck to you but the rest of us aren't.