Tomato: Explain QoS Settings?

I read the "Using Tomato's QOS System" tutorial and maybe gained some more knowledge, but I still have a gap in my understanding.

First, I want to be clear on the Outbound Max Bandwidth. This is really my upload speed multiplied by .85. And Inbound is my Download speed. It is easy for me to get the two confused.

Please explain what the two columns are for "Highest". I'm not sure what 80% - 100% means.
What happens when 80% is reached?
What happens when 100% is reached?
What if I choose no limit? Is that the same as 100%

Thank you,
Jake