Does the pork have to be cubed if you are going to shred of anyway? It seems like a lot of extra work.

This recipe is somewhat backwards; it is absolutely essential in carnitas that the meat is browned AFTER it is cooked; the crust that this forms is the major defining characteristic of the dish. Homemade versions of the dish vary in technique- it is best deep fried in lard, in which case it should really be done in large pieces, but people make versions that involve shredding and browning in the broiler in a fairly shallow baking pan. This is a better than nothing method, but probably your best bet in this case.

They are cut up into small pieces so they cook faster.