Just to add to what's been said previously.
If the service is there, use it--it may save your arse one day.
As for the case you relate, if the instructor was PIC then it's his decision. Conversely, if you're flying P1 or P1US then you're responsible and you have the authority to do as you see fit.
Lastly, if you're not comfortable with something, bring it up during the debrief, maybe follow up with the CFI if still not satisfied. Having said that, keep in mind your instructor will
generally know better and try not to make an anal cavity of yourself unnecessarily.
