> In this case, allowing 20,000+ contacts does not reduce anything for the rest of their user base; it only positively impact some heavy (and presumably loyal) users of their system, which nets in total increased satisfaction.
This is oversimplification. Knowing google, they would want to track different users' contacts and mutual contacts, and email frequencies habits etc. Contact size, is larger than O(N) complexity.
This is oversimplification. Knowing google, they would want to track different users' contacts and mutual contacts, and email frequencies habits etc. Contact size, is larger than O(N) complexity.