Office is and has been a core application for a quite a while within most Windows environments. This is a small list of things that have been adopted to make the user experience better for users not located close to the file-servers, or articles that allow you to understand why things happens.
Slow network performance when you open a file that is located in a shared folder on a remote network computer
Known issues with Office if Desktop or My Documents is redirected
An Office program is slow or may appear to stop responding (hang) when you open a file from a network location
Excel workbooks may open slowly over the network
Slow performance when you browse the My Documents folder in the document library in Windows 7 or in Windows Server 2008 R2
and for the PST / OST-files;