It is normal/standard to put 'flyback' (at least I think that is the technical term) diode to provide a path for current to flow when you turn off a coil.
De energising a coil, the collapsing magnetic field will create a voltage oppisite to the one applied. In a circuit, the current will flow through any path available. In transistor switch circuits, the transistor needs to be capable of withstanding the high voltage.
So it is normal to provide a path for the induced current to flow back.
In the circuit shown, it is not well drawn for beginners to understand. There is a connection to positive voltage near the coils. The diode in series is the current return path only.