Sometimes working on a network file is easier if you first copy the file to your local hard drive. Then you can access it from your application program more efficiently because you don't have to use the network. This is especially true for large database files that have to be sorted to print reports.
You're asking for trouble, though, if you copy the file to your PC's local hard drive, make changes to the file, and then copy the updated version of the file back to the server. Why? Because somebody else may be trying the same thing at the same time. If that happens, the updates made by one of you-whoever copies the file back to the server first-are lost.
Copying a file to a local drive is rarely a good idea.