In a motor where both the field and armature are wound there are at least two possible control scenarios.
The field winding can be excited with constant current and the armature voltage controlled, this is similar to a common permanent magnet DC motor. There is back EMF generated at the armature.
Alternatively, the armature can be excited with constant current and the field winding controlled. Apparently this configuration allows the torque on the motor to be controlled with a small amount of power at the field winding (and high current at the armature) why does this contrast with the original scenario? Finally, is there any back EMF in the field winding?