What is Windows activation?
Activating Windows 7 installation is in a way registering Windows 7 operating system of yours and making it legal.
Since Microsoft is keeping their rights on their various products including Windows products using the genius activation method, as a Windows 7 user, you should also activate Windows 7 copy of your own within a given period using one of different methods.
Why activating Windows 7 is important?
Microsoft operating systems had this feature on Windows Vista editions as well as on Windows 7 editions with different Windows 7 Build 's until its RTM release is published.
And windows activation which is not completed in the given period of time disables some Windows features and prevents you to use all properties of your system after the activation period.
Also you may not be able to update your system with the recent product updatsd from Microsoft.
So to make sure that you can benefit from all the feaures and enhancements of your Microsoft Windows 7 operating system, give priority to activate Windows7 as early as possible.
If you have already tried to activate Windows 7 copy, but failed and getting "This copy of Windows 7 is not genuine" warning then you can refer to Windows 7 troubleshoot article Windows 7 Activation - This copy of Windows 7 is not genuine for possible solution suggesstions.