A pitchback is used to reverse direction and gain some alt, preserving E as much as possible. Its most useful with the enema breaks flat after the merge, or breaks low, since you can get guns on quicker than if you jst pulled up and through in an immelman.
A Yo-Yo is used to prevent an overshoot on a rear quarter pass when the target breaks, you pull up then turn into the target, part of your radius if turn is the vertical component, keeping the flat radius as small as possible. The Yo yo also puts you back at an alt advantage, and cuts your airspeed letting you do a more controlled pass from above and behind him.
Damn, I sign on for a day to look for old names, and its like the AWTA again.