....there have indeed been (well-publicised) compulsory call-ups for Afghanistan (65 in number from my former unit at the moment). I suppose it depends on the role of the unit you join, but my former unit (role = Movs, dare I mention it on this forum!!) are primarily used as "backfill" for Regulars on OOA Ops - so you will find the majority sitting watching TV in the crewrooms of a certain couple of AT bases at the moment.
Why's that....of the call-ups I've been involved with (this would have been the 3rd), they've all been too late for us to really help out when the workload was at it's height.....that's one for the politicians to sort out though!