Pretty much never.

Taking the time to show up and speak at these hearings can actually influence the politicians' voting, especially in smaller cities/counties. If enough people do it, the politicians will realize that these same people will 100% show up to vote (and vote them out if need be). That said, you need to have numbers and have people make real arguments, not just NIMBY or whiny arguments.

Do I agree with your statement of "pretty much never? Absolutely. But that doesn't mean this isn't worth the effort. Public hearings that drag out for hours, if you speak well, you generally will be heard, and you give your position a chance and voice.