Relative axis control would allow self-centering inputs like controller sticks to effectively be used for throttle control.
Modifier buttons would allow additional buttons/axes to be bound.
Example: Relative axis control would allow a twin stick control setup similar to an FPV drone, and a modifier button can be used to enable free look with one of the sticks.
Idea shamelessly ripped from Helicopter Gunship: DEX. It works amazing in that game for flying helicopters.
Side note: That game's use of 2 modifier buttons to create 4 layers of control binds is brilliant.