Page "Double-barreled shotgun" Paragraph 5

One significant advantage that doubles have over single barrel repeating shotguns is the ability to use more than one choke at a time.

Some shotgun sports, such as skeet, use crossing targets presented in a narrow range of distance, and only require one level of choke.

Others, like sporting clays, give the shooter targets at differing ranges, and targets that might approach or recede from the shooter, and so must be engaged at differing ranges.

Having two barrels lets the shooter use a more open choke for near targets, and a tighter choke for distant targets, providing the optimal shot pattern for each distance.