https://support.box.com/entries/20366301-Box-Sync-FAQ

Some select Limitations and Recommendations from the FAQ:

2 Limitations

2.1 File types blocked by Sync

The following file types are blocked by Sync:

Temporary files and folders (.tmp and files/folders starting with ~ character)

System and hidden files

Windows shortcuts

Box WebDocs

Outlook PST files

QuickBook files

Google Docs/Spreadsheets

Note: Hidden folders will be synced. Hidden files are not synced.

Versions Affected: All

2.2 Long file paths

Windows does not allow file paths longer than 256 characters. For this reason, Box Sync for Windows will not download any files that result in a path length of more than 256 characters. To prevent this, we recommend moving folders on Box to limit deep folder hierarchies.

The full path of Microsoft Office documents includes the drive letter, and all characters and folder names up to and including the name of the document. The entire path cannot be longer than 242 characters in Word, or 218 characters in Excel.

Versions Affected: All Windows

2.4 Mac bundles

Many files on the Mac are stored as "bundles", which is a folder that OS X is able to interpret as a file. This includes many iWork files, Mac Apps, NIBs, and more. Box Sync will not upload these files to your account.

Roadmap: We plan to support this in the future.

Versions Affected: All Mac

2.5 Links & aliases

Links and aliases are not officially supported by Sync. For example, Cross referencing links in Excel documents would be broken upon syncing to a different computer.

Versions Affected: All

2.6 Characters blocked by Sync

Sync does not support files or folders that contain any of the following characters:

   \/*?":<>|

If you attempt to sync files or folders containing these characters, Box Sync will prompt you to rename the file or folder using the underscore character. In most cases, we recommend pushing the "Rename" button and accepting the renamed file or folder that Sync suggests.

Versions Affected: All Sync

3 Recommendations

3.1 Do not sync a large number of files and folders

Syncing a large number of files and folders can degrade your computer's performance. For this reason, we do not allow users to exceed the limits below:

Optimum Performance: 10,000 files & folders maximum

Technical Limit: 40,000 files & folders maximum

All previous versions: No more than 10,000 files & folders

Roadmap: We plan to increase these numbers for future versions.

Versions Affected: All

3.4 Do not install on Windows or Mac Servers
Although some users have reported successfully installing Sync on Windows and Mac Servers, this configuration is not officially supported by Box.
Versions Affected: All Windows

3.4 Do not install on Windows or Mac Servers

Although some users have reported successfully installing Sync on Windows and Mac Servers, this configuration is not officially supported by Box.

Versions Affected: All Windows