We’d have to ask someone with more practical experience, I guess…for me it’s like a gut-feeling; something like inconsistent Normals in a Mesh.
In the screenshot I provided, I indeed made 2 Armatures, one Scaled negative 1 0n the X-Axis. But, bad as that would be, to have something like that in 1 Armature? My bones ache, when I try to imagine something like that 😱
But, I cannot explain exactly why it would be bad.