Fat is energy. Heavily muscled pigs will generally use fat or energy to fuel growth and muscle synthesis until they reach the point in their growth curve when they begin to lay down fat.
So, it depends upon the size of your pig. However, with that said, early in the growth curve you can cause pigs to lay down more cover by "overriding" their energy requirements. Simply, just give them more energy (in the form of fat) than they need, and they will begin put on some cover.
Moorfat is not one of our products, but when I've seen the product it is a powder, so if you put it in a self feeder it will sift down to the bottom of the self feeder and the pigs are not going to see/eat much of it.
If you have the power to do something positive for somebody.....use it