On redundant wiring, it would depend on your application and how critical a failure may be. Normally if the correctly rated relay is used, it will be pretty dependable. The question is how redundant are you talking about?
You could have two relays in parallel connected together at the same point which would share the current load when both are working correctly, but if you loose the connection from the switch, or if they are using the same ground, fuse or circuit breaker, then the redundancy is limited.
Also, when designing a redundant system you would want some way to test or verify both paths are working correctly.
I would guess most redundant wiring would be used on endurance racing vehicles where the extra cost and weight is not a big issue.