I will give you my pros and cons from a FJ perspective:
Pros - You can practice high end war fighting in a jet with all the relevant systems working against realistic threats (I.e. not a 1970s french business jet doing 0.6M )
- You do not have the EMCON constraints of live flying.
- If you are programmed for a 4 ship sim you will probably fly a 4 ship sim, live flying not so much.
- Debrief facilities generally allow for more in depth analysis of the mission.
Cons - The main one is that you do not develop rounded airmanship in a sim, clearly a sim helps, particularly with emergency handling, but so far sims have struggled to replicate the full spectrum of challenges that one encounters in the real world.
- Flying is not just about the aircrew, deploying a sqn and running a high tempo flying programme in an austere location clearly involve a huge 'whole force' effort. Good luck with deploying a Sqn that only fly, and engineer, a couple of jets a week, especially when those systems are highly complex.
- A recent USAF report into increased accident rates listed over reliance on synthetic training as one of the main contributing factors. It would suggest that we have already pushed the boundaries of what is safe.
- You can't pull G.
My personal view? 90% synthetic in unsafe, 50/50 probably just about works at the moment. Sims complement live flying.