The importance of integration between roles on a product team can be seen by what happens in its absence. People will gravitate toward tasks they can complete without leaving the domain they own. Developers will refactor low-value parts of the codebase, designers will tweak the color of UI elements. From my own experience being in this position, there’s usually a thin vaneer of justification for these tasks. But it delivers nowhere near the value of combined efforts on customer-facing features.