You'll get about as many answers to this one as there are shooters! Barrel length is subject to each shooters preferences and everyone has different reasons for why they like what they do!
I've always been a lousy wing shot, never made any difference what barrel length I used. Until I got my hands on my Crescent 12 bore! It has 30" tubes and I can hit anything that moves with it!
I have found that I can shoot just as fast with the longer tubes as I can with the coach gun barrels and more importantly, I can hammer those extra point flyers every time! In many cases the longer tubes give an advantage too! When grabbing for a staged gun most pards have to bend down a good bit to pick up a short scatter gun staged in a rack or against a door frame. I don't! I can grab the upright barrels, turning and tilting them away from me as I lift and bring the grip up into my other hand. As soon as I have the wrist firmly held I can let go of the barrels and grab fer my shells! No time wasted bending over and straightening back up! :grin:
However, I personally think that length of pull and comb height is far and away more important to good scattergunning than barrel length! If the stock fits properly, you will shoot good, no matter how many inches of tube are hanging out there! My long barreled Crescent just happened to have the right stock fit for me! So I'm happy! :-D :-D