Most non-pet jobs can fit their basic combat skills onto just the first crossbar plus expanded crossbar, but some players like to have more than the bare minimum (with extra slots for macros, target marking, etc.). Between that and the jobs that do have the extra commands for controlling their pets, there's reason enough for at least some players to be swapping between multiple main bars.

Anything that improves clarity in those cases would be a good improvement, even if it is possible to just avoid that situation in many cases, so I like this suggestion.