http://www.symantec.com/business/support/index?page=content&id=TECH102686
You configure clients to be in either user mode or computer mode, based on how you want to apply policies to the clients in groups. When you add a client, it defaults to computer mode, which takes precedence over user mode.
If the client software runs in user mode, the client computer gets the policies from the group of which the user is a member. If the client software runs in computer mode, the client computer gets the policies from the group of which the computer is a member. Many organizations configure a majority of clients in computer mode. Based on your network environment, you might want to configure a few clients with special requirements as users. You set up clients as users or computers by adding the users and computers to an existing group. After a user or a computer is added to a group, it assumes the policies that were assigned to the group.
computer mode: The client protects the computer with the same policies, regardless of which user is logged on to the computer. The policy follows the group that the computer is in. Computer mode is the default setting.
user mode: The policies change, depending on which user is logged on to the client. The policy follows the user.