From the HBR article Why Teams Still Need Leaders:

 Members of agile teams still need to coordinate and find ways to resolve conflicts. Even if you’re not using hierarchy, you always need a decision-making role. The question is, how can you encourage working together and coordination in a simple and elegant manner?

I second the importance of decision-making. Tip-toeing around as no one wants to or feels designated to make the call, is such a common way for groups to procrastinate.

We are all familiar with the situation in private life: a few people are together, some ideas about where to go next, dinner, drinks, etc. are being floated. Because there is not really someone particular in charge, bearing any responsibility to satisfy or feed the group, and no one wants to be impolite, imposing on others (people play the “I am easy.” card), the decision can be dragged out.

In a team though, as a group with a common objective, decisions have to made efficiently. Whether the team always the same person in charge (fixed hierarchy), or the group actually has the flexibility to designate the person with the most expertise and competence regarding the issue at hand – both approaches work.

State the problem in the negative, and it becomes clearer:
When a team does not have a way to make decisions, it will not make much progress.