Ideal Length Barrel for a Slug Gun

What is the ideal length barrel for a slug gun? Is there any real advantage of longer over a shorter barrel? Thank you.

Most all powders used in 2 3/4″ shells will achieve full velocity in a 20″ barrel.
Some 3″ slugs may need up to a 24″ barrel to achieve max. Velocity.
If they are fired in the shorter 20″barrel they could lose about 90 ft/sec.

Cold temperatures (10 degrees or below) will have a much greater velocity loss, in any length barrel, than the difference between a 20″ and a 24″ barrel gives you at 35 degrees and above.
Muzzle blast/flash is always more in shorter barrels.
20″ barrels are much nicer to hunt with.
I hunt with a 22″ barrel.