You should definitely check all avionics before you start to taxi.
Obviously some things can't be checked e.g. if there is no receivable VOR then you can't check that, but you should still tune in a VOR/DME if it is to be used after departure.
For an IFR flight, you need to start ahead of the plane and stay that way.
Also, in some scenarios you may depart from an airport which is below minima for getting back in right away, etc.
My new instructor has not mentioned any of this and no checks are ever made
