For some gliding purposes, recording the type of launch – aerotow, winch, catapult etc. (there are others too!) can be important. The gliding logbook has a column for this. People who use a power logbook and spare columns or whatever would be well advised to at least make a note in the remarks section, in case e.g. currency on type of launch comes into question. Really, separate books are better for most purposes.
There can be an issue of which to use for certain flights. E.g. on my gliding instructor training course, before I had done any power flying as such, we used a small powered aircraft for some spin training, to obtain a higher rate of rotation than happens with most gliders. I had no choice but to record it in my gliding logbook.
If you fly TMGs at some point, they might count as gliding (like SLMGs) or power. I did some of both – when flying a Falke as a glider (Instructor doing the power bit) I put it in my gliding logbook. When obtaining what was then a class D to add to my PPL class A, it went into my power logbook. Under EASA, I don’t know how that will evolve or be clarified.
Hope this helps.
Chris N.