Thinking about it, in any environment a Mayday would be the last thing on my mind, especially out of controlled airspace. No use waffling on the radio, it's not really going to get you any help. In a light aircraft it may be of use if you're lost (D&D in the UK), but apart from that you fly the aircraft. The only time a mayday will be useful is to alert the crash services, although having the freedom to take any route to any runway would certainly be useful, and would definitely help you in a ditching scenario.