Why does the Las Vegas Airport have three control towers?
One of those is the old tower, built in 1983, and scheduled for demolition.
(in the bottom left of the picture)

The location and height of the old tower created blind spots, which were covered by the much shorter ground control tower attached to the D Gates. (upper right of the picture)

The new tower is in a better location, and tall enough that it doesn't have blind spots.  I couldn't find a reference to if the D-Gate mini-tower will continue, or be demolished.