Selective Sync is a feature of the Dropbox desktop application that allows you to select only the folders you want to be synced to your computer. Selective Sync gives you the control to ensure you have only the files you need on any computer. It's especially handy if you want to save space on netbooks and other computers with small hard drives.
To enable Selective Sync, head to your Dropbox preferences from your desktop:
A window will appear with a list of all the top level folders in your Dropbox folder. The folders with a check next to them will be synced to your computer. Uncheck any folders that you don't need to sync to your computer's hard drive. When you're done, select OK. Any folders you deselected will be removed from your hard drive, but will still be available through the website and on any computers linked to your Dropbox account.
Use the Advanced View button to drill down into the folders in your Dropbox. Click on the arrow next to the folders in your Dropbox to drill down and check or uncheck folders deep within your Dropbox hierarchy.
Folders that are deselected in Selective Sync preferences will be removed from the Dropbox folder on your hard drive. However, if a folder is created with the same name in the same place as the unsynced folder, the new folder will appear with a gray circle and a minus sign overlay. This icon indicates the folder is not being synced to your Dropbox. If you resume syncing your old folder of the same name through Selective Sync preferences, the new folder and its contents will appear alongside the old folder and have "Selective Sync conflict" in the folder name.
Deselecting a shared folder from your Dropbox Selective Sync preferences will only prevent syncing to your computer. The shared folder will remain synced and active in the Dropbox of other members of the shared folder. To remove yourself from a shared folder, you can either leave the shared folder from the Dropbox website or, if you are the owner of a shared folder, you can unshare or kick out a member of the shared folder.
If you are running the Dropbox desktop application for the first time, you may have to wait until Dropbox has finished indexing the files in your Dropbox folder before you can access Selective Sync settings. If you see a message that says "Performing initial sync with server. Please wait...," it means the Dropbox desktop application is in the process of indexing the files in your Dropbox or you have paused syncing from the Dropbox menu. You can choose to wait until indexing is complete to access your Selective Sync settings. Otherwise, select Cancel to dismiss the message and return to your preferences window. If you have paused syncing, you can resume syncing via the Dropbox menu.
Dropbox will continue indexing (as indicated by the blue icon with rotating arrows over your Dropbox icon) and you will still be able to browse and change other preferences while Dropbox finishes.