Agree that a bead isn't generally neccessary.
I've noticed when shooting Sporting Clays in particular, that in very
low light conditions, in mottled shade and against difficult backgrounds,
a bead that you can see is often beneficial in establishing the barrel to target relationship, however. ( Black rabbit targets over bare earth in shade is one example that comes to mind ) In such cases, one of the magnetic "Truglos" that simply go on over the rib IS handy, and WILL help your scores. Have used one at first light and last light when waterfowling .... it does help.
In open sky/normal daylight, a bead is just decoration. Focus on the target. With proper gun fit and good mounting technique, the gun should be shooting where you are looking .... at the target !