Multiple sensors don't increase the accuracy of skeleton tracking or anything like that. Each of them processes their own depth / color feeds independently and outputs the result to NI mate. You can use multiple sensors to capture data from a larger area by, for example, pointing the sensors in different directions.
If you have multiple sensors facing the same direction you should note that they will interfere with each other. This is due to the infrared grid being fired by both sensors and them each then not being clear on which grid is projected by which sensor. This will apper as increased noise in the depth data.