Think of a remote-first collaboration arrangement. In such scenario the concentrated communications become vital for collaboration efficiency.
'Old' approaches could work too, emails can be typed and sent with a right set of CC, also IRC can be set up for chats, teams can roll their own messaging tool of choice.
It's all about policies and consistency in adhering to them. When these features are devised together as part of a tool, it offers to a client those policies out of box. Thus, feature planning or collaborating on a merge request becomes more transparent, perhaps more real-time, when the tool supports the 'social' features.
Just a feature as simple as "@user" mention notifications may promote the level of collaboration.