Tarun Chitra provided an excellent description of when governance is needed within DAOs in his recent piece for a16z,

This could occur in many different ways: For example, all organizational decisions could be determined by tokenholder voting, but token ownership and voting turnout could be widely dispersed among many “minnows” (persons each holding a small % of total token supply/total voting power). Alternatively, different types of decisions could be delegated... See more