I think I suggested a Contributor level member so that they could be allocated official positions in the charter.
It was also to track who had signed up to the CLA (or similar).
At the time we were discussing Silver member access to the Governing Board (in a 5-1 ratio, maximum 2 if I remember). The Contributor level member was there to allow Contributor access to the board at a suggested 20-1 ratio with some maximum, voted for by their peers.
I think this level of membership is needed to track CLA?
/Matt