On the EC120 - I don't see the advantage of winding her to flight before you run the hydraulics check, set radio frequencies, cage the AH, etc. The engine at flight idle with prime pump-off is self-sustaining so the difference I see between the two states is how fast the blades are turning / how much fuel you burn.
I use flight idle in a couple of other circumstances - rotor-running refuel, held on the ground for traffic, etc. I have not seen any limitation in the POH for how long you can or should sit at flight idle, other than during shut-down procedure.
I would be interested to hear from an engineer whether there is any difference, other than in the shut-down procedure.