Personally, I always use the training flight for the usual emergency drill practice and to try out new techniques, tips etc (pretty much the same as any flight I take with an FI).
I would have thought, however, that in terms of consumer law in the UK an FI would be on very dodgy ground if they undertake a 1 hour training flight for the purpose of revalidation but then refuse to sign off the flight (an inextricable part of the training service provision) while insisting that the flight cost be borne by the trainee.
In which case I guess the FI has discretion in not signing off the flight as long as the club (or whichever body is providing the service) is prepared to foot the bill for the flight.
The other effect that I notice with my own flying is that, when I am with an instructor I have a psychological tendency (which I have to conciously fight) to take less responsibility and care in certain phases of the flight on the basis that the instructor will pick me up on them anyway - this can inevitably lead to a level of performance comparatively below what I achieve when flying by myself or with passengers.
From the FI point of view this was often a demonstration of my worst standard of flying rather than my normal standard, thus a judgment of my overall skill level on the basis of a 1 hour flight could be very wide of the mark.
These days I actually believe I have control rather than just saying it.
Regards all, enq.