>>20927975Your main goal, outside of the super simple task of getting egg moves, is to secure IVs for offspring pokemon. A Destiny Knot, if given to a pokemon, secures the offspring pokemon will carry on 5 IVs from either of the parents in the breedings. It's hard to secure these, however, as you can't have both pokemon holding knots without an everstone.
TLDR; you need pokemon with excellent IVs, that can be judged with the judge at a respective location per game, that can pass down IVs into their offspring.