Dropbox is a file synchronization service provided by Dropbox Inc. When you save photos, videos and files to your Dropbox account, it syncs with all the devices you have connected with your Dropbox account. So it takes up space on each computer hard drive. If you want to save the space of your computer and make enough space to sync your photos, videos and documents in your Dropbox, then you can enable a Dropbox Selective Sync. To learn how to enable Dropbox Selective Sync on mac OS X, check out the steps below.