If you use Dropbox regularly, chances are you have installed Dropbox desktop app on your Mac. Dropbox for OS X will attach a “Dropbox” folder on your Mac and sync your Dropbox files in the cloud to this folder. This allows easy access to your Dropbox files from Finder or other Mac apps.
Dropbox desktop app will attach the “Dropbox” folder under “/Users/<name>/Dropbox” where <name> is your Mac username. When you place a file in Dropbox from your iPhone, iPad or from other Macs, a copy of the file will be synced into this local folder. Thus your gigabytes of Dropbox files will be eating up precious hard disk space in your Mac’s boot volume.
Dropbox desktop app by default will sync all files into your Mac. You can make use of Selective Sync feature that allows you to select only the folders you want to be synced to your Mac.
To enable Selective Sync, click on the Dropbox icon on the menu bar. Click on the gear icon and select Preferences… from the menu.
On the Preferences window, select the Account tab and click on Change Settings… button that is next to Selective Sync option.
A drop-down window will appear with a list of top level folders in your Dropbox account. You can see that by default all folders are checked to sync to your Mac. Un-checked those folders that you do not want to sync to the local hard drive of the Mac. Click on the Update button to save the settings.
By using Selective Sync, you can save the hard disk space on your Mac’s boot volume. Which also means inconvenience as those unselect files will not be available for use via the Finder on the local Dropbox folder.
You can relocate the Dropbox local folder out of your Mac’s boot volume to another hard disk attached to your Mac, On the same Dropbox > Preferences > Account screen as the Selective Sync option, click on the button next to Dropbox location. Select Other… from the drop-down menu, navigate to a new folder to change the Dropbox location.