A fairly common reason offered for having Local Files (storing them on our local PC too) for projects using Worksharing is to improve the disk drive access to data. I believed it, others have believed it, yet it isn't really true.
One of the things I've personally enjoyed about Revit is the active role the founders of Revit take in the Revit Community. So recently when yours truly, among others, offered this story...again, Irwin Jungreis could stand it no more! (kidding)
He wrote the following in a reply at the Revit forums at AUGI.
"The purpose of having separate local and central files is not to handle the network traffic, but rather to give the user control of when his changes are synchronized with those of other users." "If the only time the local file was synchronized was when you closed the file, you wouldn't be able to get other people's changes during your session, or give them your changes." "If it automatically synchronized when you closed the file you wouldn't have a way to keep your changes separate until you were ready to publish them, or avoid having other people's changes come into your session until you were ready."
Irwin, thanks for saying so!
(remember to view a thread at AUGI you'll need to log in, join)