Student conductor in high school, yes they are needed.
When our teacher was sick I was appoint conductor by the high school orchestra and school admins.
Professional conductors read the scores like a hawk as they are played. They make sure that all the instruments are playing the music right and they make corrections are needed. Nothing and I mean nothing is played without the conductors notice and approval.
The conductor serves several purposes. The first and probably the most important is to give the orchestra a steady beat. He keeps time with his baton so that all members are counting the time the same. The other thing he does is to be the “ears” of the audience in the group. He hears how the different instruments are playing, urging some to come out louder, toning others back, etc.
Absolutely.
The conductor beats time and prepares the musicians in rehearsal, but most importantly the conductor knows every aspect of the musical score that is being played by everyone else.
A conductor brings a unified vision to the music.