mik0ton succinctly sums up the importance of this document, for a successful online community.
The Community Charter clarifies for its members the general framework necessary for a successful launch, cultivation, and growth of the group.
More at Community Charter « Stop, Collaborate and Listen
Related posts:
Investing In Community: 2013 State of Community Management – The Community Roundtable 
When Community Managers Bash Other Community Managers | ManagingCommunities.com: Community Manager Blog 
Think About Online Community Moderator Escalation Policies Before You Need Them | ManagingCommunities.com: Community Manager Blog