Typically this is done in places where it is important that a person cannot have blind spots and must be able to see what a person is doing at all times. This particular setup, the sensors are probably pointed at different directions and this was the best place to put the cameras.

I have also seen where you are in a regulated environment where the regulator requires access to the feed at all times, but you don't want them on your network (China), so you put 2 cameras up at the same time with 2 separate networks to allow for this.