I usually like to limit a conflict to one type of stress, that of the main focus of the fight. If it's a gun or fist fight, that's physical, if it's a discussion or some weird spell, that's mental, if it's some negotiation or something similar, social. I only allow actions that don't fit that type to be maneuvers to aid the main actions.
I expect that the majority of conflicts would be covered by a single stress track. But I can imagine a few where that wouldn't make sense. For example, what about a scenario where one half of the combat wants to beat up the other half, while the other half wants to talk them out of it?
(You know, something appropriately dramatic like this:
https://www.youtube.com/watch?v=2G8V00SkTvY)
I would imagine that the dramatic tension in this sort of scenario would be: Can I get through to [Character X] before they beat me unconscious (or kill me)? In that case, it wouldn't make sense to break up the physical and social/mental conflicts.