Among all folders in your Dropbox folder, a simple trick can let you choose the folders that you want to sync or not with other computers.
- Right-click on the Dropbox icon in the notification area (at the bottom right corner on Windows, at the top right corner on Mac or Ubuntu).
- Click on Preferences.
- Click on Selective Sync...
- If you want to access any folder, click on Switch to Advanced view.
- Uncheck the folders you don't want to sync.
- Click on Update.