I'm a developer turned product manager, and from first hand experience, I can tell you that distraction is one concern, but easy access to chat with the devs al

I'm a developer turned product manager, and from first hand experience, I can tell you that distraction is one concern, but easy access to chat with the devs also runs the risk of 'just one more feature', or constantly revising the scope of previously discussed work too. That doesn't just get them out of the zone, it confuses them about what they're meant to build. Sometimes, it's best to just complete a user story as it was logged and then see where we go from there (or even, shudder, after it's been deployed, and actual users have gotten their hands on it).