The nice guy who provide you internet, can decide what sites are cool what others don't. So he can punish some sites to make it real slow, and then can offer you an extra fee to speed up some material.

So, a provider could decide that all the Netflix traffic will be reduce, then will offer you a Netflix package extra to enjoy a best service.

And the same with all the sites, YouTube, Google, Hulu or whatever.

Basically they can manage his traffic how they preffer without any law making they be fare (or neutral) with how they decide.

Website traffic is a set of tubes. All these tubes have the same width and the same amount of liquid can pass through these tubes. This means all the liquid that passes through these tubes have the same amount of priority, all the liquid is treated equally.

But if the provider of the tubes see that one of the tubes has more liquid go through it than others, they may think that they should get more money to use that tube. So they now offer two tubes for the same route: one tube has a small diameter, and not a lot of liquid can pass through it at once, the other route is the same size as it was before. You can use the small tube for free, but the larger tube now costs more money to use it.

Net Neutrality basically states that all tubes should be the same size, and no company should have the power to change the size of their tubes.

A non-monetary reason for this is because as a company they may prefer one tube over another, so they massively reduce the size of one tube to funnel the majority of the liquid into the tube they prefer.

I.e. They can reduce the speed of YouTube because they want you to use Vimeo instead.