Unlike other, more complete programs, it won't keep your computer under constant surveillance. It is intended to be used in the event that you suspect a specific computer has become infected.
You just have to run the application and begin the analysis on your computer, after which any detected virus will be removed.
It is an ideal application for netbooks or less powerful machines which can't cope with a heavy, power consuming full antivirus suite. By using this scanner from time to time, you can still keep your system well protected.