this is one of me favorite discussions simply because of all of the research i have personally done on cord and chain lengths. i have a system of classification that i use for myself that i like to share with others. (probably not an original system, so i take no credit for it lol )
short - 1/4 in to 3in
medium - 3+in to 6in
long - 6+in
now with short chain / cord, you have more control in swings and aerials, freestyle requires a grip that is lower on the stick.
with medium chain / cord, there is a balance between control, and freestyle usability, as well as medium abilities for combat application
with long chain / cord, you have less control, but there is an immense amount of freedom with freestyle application. the longer connection allows for more rotations for wrist and finger spins (and is perfect for the advanced finger trick, the infinite finger spin) this is obviously the hardest to style to learn, as you have the least amount of control, but when mastered, this style of nunchaku is amazing, watch some spinstorm. he uses a long chain, with shorter sticks.