sure, i've gathered the info off of lots of threads and a few websites, so I'll just boil it down.

HOW- by inserting small bits of lead into the leading edge of the controll surface, or on an extension arm in front of the controll surface, this is easy on the tailfeathers of the corsair, because they're aerodynamicaly balanced, so the lead goes in the bit that sticks out in front of the hinge line. also lightening the back side of the surface means you need less lead, which means you need less lead in the nose. pic attached of the rudder

WHY- flutter. with long controll linkages, there's more chance of getting flutter from flex/slop in the linkag system. the best way i've heard flutter discribed is with a simple experiment. take a 1 foot ruler with holes in it (or make a stick with 2 holes) put a pencil in one of the holes near an end, to simulate the hinge line, and shake the pencil up and down (or side to side, depends on how you hold it) the ruler will twirl arround the pencil very quickly. now stick a bit of lead or whatever else on the short end to balance it, and shake again. won't spin will it?

the spinning is basically the same forces that cause flutter, but since there's a linkage the controll surface oscillates (flutters) and if it's fast and violent enough, it will rip the plane in half. quickly.
balancing the surfaces, even partially, will stop flutter, or at least reduce it engough that the linkages can cope with it.

that's the way I understand it, if I'm wrong, someone please let me know. (If i'm right a pat on the back would be nice, I just lost my daily flyer)