This is best described with an excerpt from Agile IT Org Design:
In the absence of clear assignment of accountability, we often get collective owning of authority and collective disowning of accountability. Collective ownership works better within a team, and the most common example is collective code ownership in development teams. However, there is clear accountability even in the context of collective code ownership. The question “Who broke the build?” fixes accountability unambiguously when version control and continuous integration are in use. Besides, even within Agile development teams, things aren’t so egalitarian. The tech lead has ultimate authority and accountability (ownership) for technical design decisions. The product owner has ultimate authority and accountability for what goes into a feature. Collective ownership of business outcomes across teams is an order of magnitude more difficult to achieve. Kudos to those who can pull it off. For the rest, clarifying ownership is a first step to improving organizational agility.