There's a great blog post by Patricia McDonald on BBHLabs' blog discussing the role of campaigns in today's conversation and platform-led digital world. Here are three important/salient points:

Campaigns start conversations: Campaigns are the jokes, the chat-up lines, the anecdotes that get conversations started...Campaigns bring people to platforms.

Campaigns refresh and expand conversations: ...1. to give those people something new to talk about and 2. to draw more people into that deeper relationship.

Campaigns amplify conversations: Campaigns can give [passionate] users and their content a much broader stage to play on.