One would expect that the bigger the network, the more value users derive from it.
However, as networks scale, the value for users may drop for several reasons:
Connection: New users joining the online community may lower the quality of interactions and increase noise/spam through unsolicited connection requests.
Content: The network may fail to manage the abundance of content created on it and may fail to scale the curation of content created and the personalization of the content served to users.
Clout: The network may get inadvertently biased towards early users and promote them over users who join later.
Just as network effects create a rich-becomes-richer cycle leading to rapid growth of the network, reverse network effects can work in the opposite direction, leading to users quitting the network in droves. Friendster, MySpace and Orkut bear testimony to the destructive power that reverse network effects wield. (Source)