Your voice is your most critical self-defense tool.
In this news story, a woman out walking was assaulted. Her screams attracted the attention of another woman, who came to her aid. They were then able to fight off the attacker, who ran. According to this report, the woman was not seriously hurt but was shaken and upset.
And that illustrates Reason #2 (of 6) of why your voice is important: because it can attract attention. Attention can mean help. Help can thwart an attack. Thwarting an attack can mean less pain and a shorter recovery time from trauma.
Attracting attention sometimes also results in the attacker getting caught. And attackers don't want to be caught. What do you want?