My current computer case (a Cooler Master HAF XM) has a front fan, a rear fan, two top fans, and a side fan, so it has very impressive airflow, and most cases in recent years have a similar number of fans, but few cases today have side fans; they still have front, rear, and top fans, so why do they not have side fans? Is that so that they can have clear glass panels to display the internal components of the computer, or are side fans simply no longer necessary?

What does everyone else say about this? Why do computer cases rarely have side fans, recently?