Long, short story:
Am bad-to-average FPS gamer, looking to improve. Saw an OSU! gamer flinging its “shots” left and right and tried my best to mimick the experience in an FPS. And it worked significantly – all of my shots felt more “secure”, even with my aiming being rusty beyond belief.
And the “trick” to do this is simply leaving your “aiming hand” to aim (ONLY) while leaving your “non-aiming hand” to shoot and everything else. That’s it.
That is an interesting take, which (also) makes sense – each millimeter matters when you are using a weapon that demands the most precision in order to hit your targets. And multitasking with your “aiming hand” can mean the difference between being able to hit your target or not. Even so while burst firing.