Using Settings on 2IS like AV and M

I'm new using my Canon 2 IS and have noticed that I can select AV and get a pre-read on the aperature and speed and than switch to M and make some adjustments. Does anyone use that or other approaches for getting a pre-read through the viewfinder?

Push the shutter button halfway down in auto, P, Tv, Av, or M and you will see the shutter speed and aperture at the bottom of the view finder or the bottom of the
external LCD if it is out for viewing. Then push the button all the way down to take the picture. In Tv you can manually change the shutter speed, in Av you manually change the aperture and in M you can change either one. Have fun learning your new camera.