To protect your session, you can assign a password. No user can access and without entering your password.
Your files will also be protected from users to the limited powers that can not be accessed.
1.Click the Start button and then click Control Panel.
2. Double click User Accounts.
3. Click on your account.
4. Click the Create a password.
5. [...]

At home or at work, you are more users to use the same computer. Now everyone wants his space, his own officers, its screen, its shortcuts, … It may happen that a user takes a few liberties for work space at the expense of the others. And other users to waste time calling as [...]