This is not a choice in modern game development. If the tool you are using is not online, or you don't have a repository to upload your work and share it on the go with the rest of your team, you are simply doing it wrong.
Do yourself a favor and make the most of the incredible technology available nowadays! Even a sketchbook should always be scanned or captured with a camera and archived in digital format. Do it now, and thank yourself for having done so in a few years! Common problems with offline documentation include files getting lost, documents shared via email and then being updated only on one end, difficulties in tracking the document version and change history, difficulties accessing files from different locations, ...
