What is the purpose of the Common Files folder in Program Files?

According to MSDN:

Common Files Folder A folder for components that are shared across applications. Typically C:\Program Files\Common.

Common Files Folder (64-bit) Same as the Common Files Folder, but for use only with 64-bit installers.

A slightly different definition is provided in the book Microsoft Windows XP Power Pack by Stu Sjouwerman, published Apr 4, 2003:

The Program Files folder is home to 16 subfolders:

• Common Files. This folder contains files shared with the Microsoft applications [sic].

I feel that folder exists mostly because MS wanted a place for its own libs shared among many programs - although it doesn't seem to get used by MS very much either!

In practice, few applications use it.

Maybe it is a requirement for an application desiring to obtain a "Designed for XP/Vista/nnn" logo(?) that it should use that folder to store files that are common within the application (this is speculation on my part - so don't take my word for it!).