Fair enough, and actually a reasonable question. What was not in the answers is one of the primary functions of the RA is in terrain avoidance, preventing CFIT, so it only comes alive below 2500' above terrain. In this time, it is hoped there is enough time to provide GPWS warnings over any terrain. The only other time it becomes useful is on final approach, usually below 1000' onwards for stabilisation checks, and is totally relied on for autolands and all the associated calls and automatic actions that take place like commanding throttles closed and flare to commence.