Unless you are very new on type, unfamiliar airport or expecting a very short taxi or flying an A380, it’s not very professional nor considerate to do the flight controls check before taxi. First you are not being efficient ( burning more fuel,) and also you are delaying other traffic behind you waiting to taxi or to push back as for example this morning; I had to wait a few minutes for this aircraft to push and start to enter my gate. If they have done the flight controls check it would have been another 30 seconds more. And yes every second matters in aviation.
