I'm happy lowering them anytime, anyplace, anywhere...
Flap assymmetry is much more a 'big aircraft' problem than one for light aircraft. Most light aircraft have a torque tube which ensures that flap travel must be symmetrical (unless something truly disastrous happens, in which case the problems will be much more serious than one flap slightly lower than the other!).
One other reason: carrying out a forced landing, it may be necessary to use a combination of configuration changes and S-turns, possibly on very short final approach, and if you haven't taught your stude that it's OK to do so, then you introduce a new hazard...
