Longer barrels give you longer sight radius, better balance, more weight "out front" which tends to make it easier to hold steady for off-hand shooting.
Better velocities can be obtained but that isn't an issue in this sport.
Short barrel carbines were designed for use by the cavalry, so unless you plan on riding up on a horse and pulling it from your scabbard, pretty much wasted intent.
Modern versions are really marketed for being "handy". Great I suppose if your shooting from a bike or quad, or hiking in dense scrub, BUT, you'll be handicapping yourself in this sport. Plus, if you turn up at a shoot with a 16.6" barrelled .357 stoked up for the rifle rams, please don't shoot next to me, the muzzle blast will be woeful. I had a bloke shooting next to me with a 20"' barrel firing Federal factory .357 rounds at the last competition I went to. Man did that thing bark, everyone on the line was commenting on his loads, wondering how much he had them "loaded up". He did offer me his empty cases as he didn't reload, they were gratefully accepted. I wound up with 196 nice, once fired, nickel cases, I use them in my S&W 686.