Most importantly a conductor serves as a messenger for the composer. It is their responsibility to understand the music and convey it through gesture so transparently that the musicians in the orchestra understand it perfectly. Those musicians can then transmit a unified vision of the music out to the audience.

Does an orchestra actually need a conductor?

Because most of the orchestras in the world can play together without any conductor. You are there to help them play better musically, and help them make a sound that is more coherent, that makes more sense from the composer's point of view.”

What would happen if an orchestra didn't have a conductor?

Without a conductor, each musician would resort to his or her own individual opinion. ... Sometimes, especially in the case of piano pieces, the conductor can give enough guidance by playing the solo part and can "conduct from the piano", but this isn't common.