The Pre-flight check will verify that a file will be accepted by Box before you send all the bytes over the wire. It can be used for both first-time uploads, and uploading new versions of an existing File (on /files/[id]/content).
Preflight checks verify all permissions as if the file was actually uploaded including:
Folder upload permission
File name collisions
file size caps
folder and file name restrictions
folder and account storage quota
Required BoxFile The attribute name is requied.
BoxFolder The _id attribute is required.