Mode C is altitude reporting.
AFAIK, Mode C should be activated whenever the transponder is turned ON. I know of no standard procedures where the "altitude off" setting is used, other than in direct response to a specific ATC request.
Our procedures also state that Mode S/TCAS be selected when the Before Takeoff Checklist is accomplished. That is usually done when approaching the TO end of the runway. Since
AFAIK all commercial aircraft DO have RA inhibited on the ground, the OP's question is moot unless there is a system failure. I don't know if the bandwidth limitations mentioned by FlightPathOBN are related to TA or RA, but seeing a target near or on the runway when on final approach may make visual confirmation of a runway intrusion that much easier...