If you just joined or left a Dropbox Business team, you might receive a notification that says that Dropbox “needs to sync your files again, which might take a while” and that “your current files will be saved in Dropbox (Old).”
This means that Dropbox needs to re-sync your files to your computer in order to make the transition into or out of the team. To keep your files safe during this process, Dropbox renames your Dropbox folder in File Explorer (Windows) or Finder (Mac) from “Dropbox ([account name])” to “Dropbox (Old).” Then, Dropbox creates a new folder in the same location on your computer and syncs your files there as well.
The result is two folders. This process is just a precaution to ensure that a copy of your files are safe on your computer while your files are re-syncing. It’s recommended that you don’t touch the “Dropbox (Old)” folder while this process is happening. The time this process takes depends on the amount and size of your files. After the process is done, you can delete the “Dropbox (Old)” folder from your computer and start using the new “Dropbox ([account name])” folder.