If you run more than one project — several products, or one per customer — switching between them to check for new conversations wastes the day. The unified inbox puts them in one queue.
Open conversations from every project you have access to, in a single list. Filter it to your own (My inbox), everything (All), or Unassigned, and narrow to a single project when you want just one.
You answer from there directly. Each conversation still belongs to its project, so replies go out with that project's sender identity and settings.
It suits a small team covering several products, and agencies handling a project per client. The pattern it fixes is a specific one: the project nobody checks because it's quiet, where the one conversation a week sits unanswered for days.
It helps less when teams are genuinely separate. If different people own different products, each working their own project keeps ownership clear, and a shared queue mostly adds noise.
Assign as you go. With one project it's obvious who's dealing with what; across five it isn't, and the unified inbox makes it easy for two people to answer the same conversation.
And check which project you're in before writing. The context that keeps you from confusing two products is a small label on the conversation — easy to miss when you're moving quickly.