The pro's are that it reduces the possibility of flutter and also reduces the potential severity and damage should flutter occur. That, in and of itself, has led me to balance the canards on my Euro and the flying stab an the AD F-16 I built for a friend.

The cons are that it is often not really necessary (although the only way to tell for sure is to fly the plane without it, and if there's a problem, its usually fatal before you can do anything about it), it is often difficult to fit enough weight into the surface to balance it, it makes the airplane heavier, and when done to the stabs, makes the plane more tail heavy - which can require additional nose weight to counter-balance...

Bob