power off is a valid and necessary technique.
Absolutely and is the normal technique in flying schools throughout the world for most training types. The term: 'power idle' is correct (sorry to nitpick, forgive me). Not to be forgotten is that the POH landing distances are given using power at idle for most light types. Many aircraft however do benefit in handling with additional power. Even the ubiquitous C172, some find the weight of the nose with the power idle too heavy, and so the addition of power is needed to assist. This should be discovered by the instructor during the 'effects of controls' exercises of course.