I have been asked many times about the difference between User and Computer categories in Shopping and for what scenarios they are most useful. Well, here goes...

User Categories - These allow you to do two things; 1) Group you applications into logical groups and 2) to restrict the user's ability to see these applications and therefore shop for it. So, an organization can bundle their applications into user categories, as follows. All applications would be grouped within each category which are shown on the Shopping web browser down the left hand side. This makes them easier to find. You would want all users to be able to see the free utilities, so no restrictions would need to be added here. However if you have Windows Security groups for development, sales and marketing users, then you can restrict the User Categories as well so that only people from each group can see the whole category.

Free Utilities 
Developer Software
Sales Software
Marketing Software

Computer Categories - These allow you to restrict access to Shopping Applications based upon the machine from which the request is being made. This is done on an application level. For example, Joe works in marketing. His user permissions allow him to shop for 8 applications which have been added to the Marketing Software User Category, however his PC is located in UK. Unfortunately UK PCs are not licensed for 3 of the applications in the Marketing Software User Category. Joe will therefore only be able to shop for (and see) 5 out of the 8 applications. i.e. He will only be able to shop for applications for which both his user and his machine permissions allow him.

There will be changes to Computer Categories coming soon, which increase the capabilities of branch administrators to manage applications at a branch/computer level. More info to follow as we approach release (Q4 2009).

Read the complete post at http://www.1e.com/techblog/post/2009/07/20/Shopping-User-and-Computer-categories-explained.aspx