Do you want some documents, such as just those files you use at the office, to remain only in your Box account but not be synced to your local computer? You can be selective about what your local Box Sync app slurps from your Box account. There are two ways to do this.
When using a browser in your account on the Web, for each folder you can right-click an options arrow located next to the Share link and choose Sync Folder to Computer or else Unsync. This includes or excludes the entire folder for all your synced devices.
If you don’t want certain folders on a single local system, you can also delete the folder from your Box folder on that local system. Deleting a folder in your local system does not delete the same folder on Box; it will merely unsync the folder, remove it from your local system, and keep it saved on Box. However, if you want to delete this folder in both locations, you need to explicitly delete the required folder in your Box account on the Web. This behavior protects content from unintentional and accidental deletions.
A special note: This behavior only applies to folders. If you delete a file in your local system, you will automatically be deleting it from Box as well.