My discovery of meatball-making started with Italian meatballs. I was taught to incorporate all ingredients together (meat, seasonings, cheese, breadcrumbs...) with the least possible amount of mixing, to not make the meat too compact. Great.
Then I discovered Vietnamese meatballs, the kind you can find in Pho. I've never made those myself, mostly because I don't like them, but they seem completely overmixed to death, until the meat becomes the consistency of hard rubber. I'm sure that's what Vietnamese are after, but I don't like that texture myself.
Now I'm making Danish frikadelles, which are little ground pork patties made from a rather liquidy/sticky meat mix (vs the dry meat mix used for Italian meatballs). The recipe (http://www.copenhagenet.dk/CPH-Map/CPH-Recipes-Frikadelle-03-2011.asp) states:
The "Frikadelle" mixture gets better the more you mix the ingredients together. It is best if you leave the mixture to rest at least an hour in the fridge - before you mix it again.
However this time I'm not sure why? What is the goal of mixing so much? What happens when you mix meat (along with milk, breadcrumb, flour, eggs and seasonings)? What happens when you mix it again after a resting period in the fridge?