In collaboration, people share decisions, thinking, resources and responsibility. It is the opposite of hierarchy which is a two-class system of power haves and have-nots. People who continue to defend the value of hierarchy would argue that there are selected times when collaboration is appropriate in organizations. In a hierarchical parent-child culture, parent figures approve of collaboration for the purpose of generating proposals for higher level approvals.
In these cases, people aren't actually deciding anything together on their own initiative. Their decisions have no power. They are simulating decisions that later become one of any number of considerations that in hierarchies are not required to be transparent.
All of this raises the interesting question of whether people who have authentic power as collaborative decision makers outperform groups without collaborative power. It's been my experience that indeed they do.