How does having multiple ATC towers affect airport operations?
At larger airports it is fairly common to have more than one tower, but it all comes down to how well the tower controllers can see airplanes.  Sometimes they have different towers for ground control frequencies and tower control frequencies, and the position of the tower is optimized for the appropriate task.  For very large airports, they may need towers in different areas of the airport to properly see airplanes at each runway.

As far as practical consequences it doesn't matter much whether they have one or more towers.  At very busy airports they split up the tower/ground controllers/frequencies because one person can only control so many airplanes at a time.  For instance, there may be one controller for the North runway and one for the South runway.  In this case, there could be only one ground controller, or there may be two or even more, depending on the complexity of the ground operations.  With multiple ground frequencies, if you need to taxi from one controlled area to another, the controller that you are talking to will tell you to hold short of a particular point and contact ground on the other frequency.  Once you contact the second controller, they will clear you to continue taxiing.

In short, it is very specific to the local conditions, and they do what they have to in order to properly control the traffic.