People would be more engaged in your speech
Won't be distracted
Makes your speech more interesting
Enhances your speech
However, unnecessary hand gestures might be distracting and annoying to audience.
Prevents people from getting distracted by anything else other than your speech
A more fluent delivery
Allows audience to think and reflect
People take you more seriously
Appears to be more confident, thus convincing.
Makes you seem more authorative
Stands out from audience
Blocks you from flying objects!
Makes speech relevant