I view any kind of fancy bead on a shotgun as superfluous- their chief value lying in how well they seperate the rubes from their money. Beads of any kind are superfluous for that matter, but I do like a small ivory or brass bead just for aesthetic reasons. Try an experiment by which you remove the bead entirely and then shoot a couple rounds of skeet, clays, or trap. I bet your scores remain the same, or perhaps even improve.
There are some applications where a sight of some type might be handy on a shotgun; perhaps in turkey shooting as somebody suggested.
But otherwise Gnoahh is spot on for any moving/flying target shooting. If you are 'aiming' a shotgun with the bead you are probably doing an unnecessary amount of missing.
First time I ever saw 'Sporting Clays' was around 1986. A dude ranch in the area where I lived was setting up a course as they catered to a lot of English clients. They brought in a sporting clays shooting instructor to set up the course and I got invited to go through his program. I thought I was a fair hand with a shotgun (ATA 27-yarder), but this guy took us to school. He shot a very used H&H side by side with hardly any finish left on it. First thing he did was remove the beads on our shotguns. We then learned how to point, swing, and follow through. We learned the importance of fit and point of impact. We came out much better shooters.
Did not mean to take the thread off course. I have several dot sights on handguns, including a Burris, that I am very fond of. But I don't think they have a place on a shotgun except perhaps on a stationary target (?).