Managing User Accounts
User accounts in Windows 7 serve two main purposes. The first is to allow different people to customize the operating system to their own personal preferences, and the second is to make sure that people can't gain access to each other's files.
For example, imagine if you sat down at the computer and found that characteristics such as the background wallpaper, colors, and menu options were different from the last time you were there because someone else had come along and changed all the settings. Similarly, you probably wouldn't want other members of your household to be able to read, change, move, or delete your important personal files.
User accounts can make sure this kind of thing doesn't happen. Through user accounts, each person who uses the computer gets to customize the "look and feel" of Windows 7 the way they want, and everyone's personal files are kept separate and private.
The other purpose of user accounts is to control what somewhat can do in Windows 7 and what kinds of settings they can change. You might not want a child or a houseguest to be able to install their own software or change critical settings that could damage the system. Making sure each user has the right type of account can prevent this.
In a nutshell, user accounts make it easier and safer for multiple people to share access to the same computer.
