It is claimed that steel shot will pattern better from an extended choke, one with a parallel section past the choke. The theory is that the pellets get a vibration or "ringing" when the choke jams them together. The extra parallel section allegedly tamps down some of this vibration resulting is more uniform patterns.
Whether this is true or not probably depends on the quality of the choke, extended or not.
I shoot Light Modified/0.015 inch constriction (extended) Comp-N-Chokes for ducks. The patterns are tight and even and murder on any duck that is unlucky enough to intersect my shot string.