Sesame Street

After finishing up Project 4, I was kind of curious about using After Effects.  I found that most Television shows use this product, or something close to it.  I was watching Sesame Street the other day with my 4 year old daughter and was noticing that they had an episode where the kids were looking out of a window.  Well it got me to thinking, aka googling, and found that through After Effects, you are able to make it look like there is a window present even when there isn't one.  NIFTY, I thought to myself.  Now here is my question to the world.  Why would they do something along this nature?  What is it's purpose?  Anyway, just curious if anyone else has taken a look into all the products Adobe has to offer.  Check them out if not, they are really cool, and Adobe's website has a lot of tutorials on them to shed some light onto there mysteries.