Bridge & your devices · Collab Sync
What's the difference between sharing a folder and Collab Sync?
Short answer: Sharing lets the other Mac browse files live while both are connected; Collab Sync keeps a real copy on each Mac and keeps them in step, so either can work offline. Share for occasional access, sync for a folder you use on both.
A shared folder is browsed live: the files stay on one Mac, and the other reaches them over Bridge only while both are connected. Collab Sync keeps a real local copy on each Mac and keeps the two in step, so each Mac can work on its copy even while the other is away.
Share when you occasionally need to reach files on the other machine. Use Collab Sync for a folder you work in on both Macs.