When you save a Autodesk Navisworks file, you have a choice between an NWD and NWF file formats.
As a rule of thumb, use an NWF file format to save the scene you created by bringing all model files together, and an NWD file format when you simply want a snapshot of your current work.
Both formats store the review markups, but NWD file stores the file geometry, while NWF file stores the links to original files. This makes NWF files considerably smaller in size. Also when you open an NWF file, Autodesk Navisworks automatically reloads all modified referenced files, which means the geometry is always up-to-date, even for the most complex models.
On the other hand, whenever you need to share the scene you created and review markups with others, it is best to distribute a published NWD file, which includes additional features such as password protection and file expiration date. The published files can be viewed in Autodesk Navisworks Manage, Autodesk Navisworks Simulate, and Autodesk Navisworks Freedom (a free viewer).