What 2 ensembles need a conductor and why?

There are a lot more than 2 ensembles that need a conductor, including concert bands (large), symphonic wind ensembles (smaller than concert bands), chamber orchestras, symphonic orchestras, br choirs, woodwind choirs, some percussion ensembles, trombone choirs, trumpet choirs, flute choirs, saxophone choirs, clarinet choirs, tuba and euphonium choirs, and any other group that has a lot of contrasting musical lines and complicated transitions. A conductor is needed in ensembles like these so that the phrasing and style can be based on one person's interpretation instead of the combined interpretations of every musician in the group, making it infinitely easier to sound like a single unit when performing rather than a bunch of musicians playing different things at the same time.