Unbelievable that some pilots actually do that.
Just the way I was trained, saw others trained, and experienced throughout my time in GA. I only worked for four GA operators. All did run-ups on the run, and all expected their charter pilots to do so.
IME, most (not some) pilots in GA "do that".
Maybe "once you're more experienced" is just another way of saying the pilot is over-confident and exhibits very bad airmanship.
And Maybe "once you're more experienced" means just that: A pilot has enough experience and can safely 1: run the rpm up to 1500; 2: check the carby heat (if fitted); and 3: drop each mag, before going back to idle.
If the aircraft is being operated daily and correctly it should take all of around 15 seconds to perform. If you've got to clear a mag or something more serious, then sure, stop and sort it out.
It certainly is an "issue" in any aircraft including light singles such as a 172, Warrior or similar. It means dragging the brakes, head inside the cockpit while taxiing instead of outside the cockpit and leads to fast taxiing even while having the brakes on.
Disagree. It may do all those things, but doesn't have to, and shouldn't if the pilot uses their brain.
"head inside the cockpit while taxiing": There are other pre take-off checks that pilots do, and all of them require the head inside the cockpit for some of the time. Are you advocating that all these be done while stationary?
The OP is training for a CPL. If a CPL can't use their judgement as to whether it's safe to do simple checks while taxiing, then god help them if they're airborne and have to use their judgement in an abnormal or an emergency.
DIVOSH!