You'll finish with: You know which one you need.
Chat is where you think. Cowork is where work gets produced. The difference matters because most people try to do the second job in the first place and wonder why they're copying and pasting all day.
Where does the work end up?
"Mounting a folder" means pointing it at a folder on your computer so it can open and save files there — like giving someone access to a shared drive.
Cowork isn't desktop-only any more — but the folder part is. Cowork runs on web and mobile too, so you can start a job from your phone. What stays tied to the desktop is anything touching your local folders: a project pointed at a folder on your computer only runs Cowork sessions on desktop, and a cloud session can reach those folders only while the desktop app is open on that machine. Read a job on the train, run a folder job at your desk.
Cowork projects are stored locally and there is no cloud sync for project data. They don't move between computers, and — including on Team and Enterprise plans — you can't share one with staff. That's the cost of it being able to touch your actual files.
Most small businesses run both. A chat project for thinking and research, one Cowork project for producing. You can link the chat project into Cowork so it draws on that knowledge.
You can say which of the two you need, and why, without hedging.