How does OTL amp get its power?

I am contemplating a stereo tube amp of relative low power(for me, anyway) and an Atmasphere 60 watter caught my eye. It will be used in the output#2 of my pre. I am currently using MC501's and a MC2300 pre to drive JM Lab Alto Utopias. I understand the transformer and the Autoformer, but how and why does an OTL amp get its power and what is an advantage to using one vs. non OTL?
Do they get hot? How easily do they clip? What is its "reserve" power? All comments are greatly appreciated.

Pepe