What is with the EV button? Its useless!

I've been driving my prius for almost 3 years now and love using EV mode. However I have never once found a use for the EV button. There has never been a time that I pushed it that it didn't tell me I couldn't use it. When I'm driving (and the car's warmed up enough) driving anything under 42 mph and releasing the gas pedal will most of the time kick in EV and I can easily keep it there unless I need to accelerate above the centerline of the throttle.

I honestly wish the button wasn't there considering how useless it is.