[ecomodded]

With a micro controller it generally controls just one panel so you would use 10 or 20 of them in a large array.
One benefit that I am aware of (there may be others) is that if you have a failure it will only effect the 1 panel/micro controller and not the whole PV array.

(I do not think they are anymore efficient then the large units just more redundant)

I am not using a micro controller so just speaking off the top of my head..