Well, I'll put another view across. Using Dick's example, someone wants to fly their two seat slow helicopter into the country's busiest airport. The controllers could be occupied during a busy sequence;the helicopter maybe posing conflict to multiple aircraft with hundreds of passengers. It may not be unreasonable to expect that helicopter to be equipped such that it's return is not garbled with multiple other targets in a confined area (one feature of mode S, as I understand it), it may be an advantage to have enhanced altitude reporting, and it may save transmission time in knowing the helicopter is on the ground, without having to actively request that information. Maybe.