Labeled Parts Of A Motor DC Electric Motor - Difference Between Series And Parallel Wiring?

DC electric motor - difference between series and parallel wiring? - labeled parts of a motor

Suppose that you have continuously) a DC electric motor - 13 hp (. The field and armature coils are wired separately - the positive and negative reinforcement are labeled A1 and A2, and the motor terminals of the field coil S1 and S2. So you have the option of a serial cable when the power for both parties, or in parallel, so that the voltage is the same for both parties.
Well, what is the difference in yield between the two alternatives? What are the intended design parameters, like the thread? I've never seen anything that explains why they choose the other.
Can someone explain?
Thank you!