For ducks, not needed. The only people who can benefit from 3.5" chambers are guys who shoot geese, and do it a lot. Geese are big birds and are often shot at long range. It is hard to get enough of the large steel pellets into a 3" shell, so the 3.5's help here.
For the guy who rarely hunts geese, like me. I just have to either pass on the longer shots, or use some of the more expensive non-toxic shot. The other alternatives such a hevi-shot and some of the bismuth loads are much better than steel, even from 2 3/4" or 3" shells. But are too expensive if you are the type of guy who can go through a case of shells during waterfowl season.
The 3.5" steel shells have some kick, but are tolerable. 3.5" lead turkey or deer loads take recoil to a different level. Considering they are shot in 7.5 lb shotguns they are much worse than many elephant rifles. I've never seen a turkey wanted to kill that badly.