Logging Engine Off TMG
 

Once the engine's off in a TMG do you differentiate in your log to discriminate between power on and gliding flight?

You can if you want, but there's no particular reason to do so. Engine on or off you are flying a TMG.

If you have a TMG rating/privileges on an (A) licence, you log flight time in your power logbook, if you have TMG privileges on an (S) licence log all the hours (including powered) in a glider logbook. If you have both you can log the hours in both logbooks if you want. Remember that TMG hours, even engine off hours, don't count towards the (S) licence recency requirements.

In my own logbook, I include comments for remembering flights with long (>1 hour) soaring / gliding - only for myself.

In parallel, there is a clear differentiation in the airplane's logbook, since engine on and off time makes a big difference in rental fees.

No need, you dont log an sep with 0.1 for glide approaches, or log asymetric work in a twin as single engine