This is a worthwhile change from a few technical aspects. Thanks for the idea, even if not originally your own.
1. The biggest to me is that it removes the need for a high current switch. Mine is corroded externally so I've been wanting to replace it.
A. Low current key and other switches are easy to find (keyed or keyless) and high current ones are less common and more expensive.
B. Running high current thru a switch is harder on the contact faces than on those in a relay, because the relay opens and closes so much faster, leading to less burning of the contact faces.
C. It's pretty easy to find a relay anywhere which can carry high current, because there is at least one in the starter circuit for almost all cars.
2. This change removes a big portion of the high current route, which is always desirable. Chafe a piece of metal through a small gauge wire and the wire will probably sever or the circuit breaker will trip and either is easy to fix. Chafe near fuel or other flammable vapors and there is much less chance of ignition. Chafe through a 10A to 30A circuit and you can blow a hole in the metal that the cable is rubbing on, or cut all the adjacent wires if the chafe happens in a bundle. Not easy to repair quickly and easily. It is also much easier to ignite whatever else is in the area.
3. Contamination is the #1 cause of failure for both relays and switches. Relays are incredibly robust on their own and being in the engine compartment one will be more protected with the high current circuit, rather than being in the wetter environment of a cockpit locker or pedestal.
4. If a relay were to fail, the work-around is to simply take a piece of wire and short the terminals together. (Use heavy enough wire, ventilate the compartment, wear gloves, and beware the likely flash.)