MarkDTN you must be referring to this setup.
All switch's and relays have resistance. The ford relay adds resistance to the battery cable. The two extra cable ends and the nuts holding them to the ford relay can add extra resistance as well as two new points for possible corrosion.
The relay itself adds an extra drain on the battery at the S terminal.
You said "it just doesn't have to rely on the long length of purple wire to get power".
The purple wire is still just as long and instead of going to the S on the chevy solenoid, it goes to the S terminal on the ford relay.
The ford solenoid is actually just a relay, because it doesn't move the starter gear like the Chevy solenoid does. Now you have both.
The first drawing below, shows the basic chevy wiring. The Purple wire from the ignition switch goes to the S terminal and activates the solenoid when the key is turned. The battery is connected directly to the Chevy solenoid.
The second drawing shows the small Bosch type relay connected to the Purple wire. Current flows from the Purple wire, through the relay to ground. Less than 50 milliamps has to flow through the ignition switch and relay.
When the relay is energized, current flows from the 12 V source through relay terminals 30 to 87 and back to the S terminal on the chevy solenoid.
This relay wiring has far less drain on the battery and is much, much easier to install.