OK, I'll give it a try and hope I get this right.
It eliminates the starter/ignition wire to the Starter Solenoid. It also eliminates a full time hot cable to the starter.
Useful when you have a small gauge ign wire, especially with the long run from a center console and/or some say heat soak loss in the wire.
Problem is resistance and amp loss in the ign trigger wire.
You run a remote solenoid, one large cable to the starter from the remote solenoid and a jumper from the starter to the Starter solenoid.
Your ignition wire runs to the remote solenoid getting it out of the high heat area, shortens the run, and requires less amps to operate the remote solenoid than the starter solenoid.
When you hit the key it closes the remote solenoid providing power to the Starter motor and the Starter Solenoid through the jumper.
Release the key, remote solenoid opens and no power goes to the starter.
But, you can't use that circuit on a PMGR starter because the solenoid stays engaged just a little too long and damages the starter or ring gear.
Don't ask me why on that one but someone here can explain I imagine.