How does a web page consume resources?

Does any activity of a web page scrolled out of sight still go on in the background consuming resources? Sometimes I see a banner or some flash commercials or videos and so on, I quickly scroll the area in question out of sight hoping it would stop consuming resources such as memory and CPU. I would even change the size of the browser so that the activity is not visible. Does it help?

I can hear music or talking if there is sound. I suppose any visual stuff should stop because no area in the screen is dedicated to it.