I haven't used rails since we got ducts.
However, I use rail movers with turntable a lot for compact high torque rotors, and for high speed rotors. I find them critical for making responsive, armoured turrets.
I can provide some examples tomorrow evening.
I could live without them if other turntables/cradles get their torque increased a lot. Preferably proportionally to their mass (ATM the smallest and biggest turntables provide exactly the same force).
Ping
@AuraFB, as I'm probably the only one who finds them important