Selective Sync is a feature that allows you to synchronise only specified files & folders to a particular computer. This can be particularly useful if you’re travelling & connecting to Dropbox via a mobile data (3G or 4G) connection. Rather than use a lot of your data allowance syncing everything, you can specify just particular folders. Also, some of your Dropbox folders, such as music or photos, may be unnecessary & use a lot of hard-drive space on your notebook.
To set up Selective Sync, go to Preferences and then click on Advanced. Click the Change Settings button and then just uncheck the folders you don’t want to sync.