Question regarding coil setups

[Electronix Hive]

ok so i am looking to build my 4 pole pulse motor and have been thinking a lot about the collection on the impulses..now from the basic view the run or power coil will create a magnetic field and then collapse sending the radinat or bk emf to the battery ok simple ssg done i get it..what i am trying to understand is what is the need for bifilar slave coils having one wire making magnetic field and other wire capturing spike sent to fwbr and to battery...what happens the the out of the first winding when set up on separate circuit like ssg ...does it also collect the bk emf as well as the second winding that goes to fwbr or is the spike induced the the second winding and the first does nothing ?