It all depends on the shot your trying for, ( example: if hovering and viewing large crowd, yaw might be best for a 360 degree view of crowd )
Where roll ( left right ) might be better for following moving target, or maneuvering around a tree or object
Where as ( both ( yaw / roll )) together might be best for beautiful flowing landscape or terrain, like free flying through the terrain.
I use both MOST of the time when flying around, when hovering I use yaw and/or roll as well as pitch ( forward / reverse ).
It is more about ( you ) and your style of videography! Or the shot you are looking for!
( but typically when having fun and just flying around, both together is best ( for me )!
Hope this helps!
Take care, Fly safe!
Jerry D
USA
( J Dot )