It is not always necessary to have all the single drawings of a project in Vault - a single PDF and a BOM could be sufficient, optionally a backup of the project. This bypasses of course the intendet worklfow - maybe a check in/out on a drawing level is an 'overkill' because of the interdependency of the drawings in a project. For Vault 'consumer' a PDF is easier to handle, one document with all the drawings, all drawings have the 'correct' version.