Dual licensed under MIT and GPL?


I see a lot of scripts that are dual licensed under MIT and GPL. I wanted some clarification on what that actually means in a website context. I understand dual licensing means you get to pick the license. My questions are:

  1. Does the MIT license mean you can do anything other than remove the copyright notice—and accept that is comes with no warranty?

  2. Seeing as MIT is so liberal, why offer GPL as an option? Surely, MIT is always better.

  3. Why do people use GPL for website scripts? It seems like a poor fit to me (if I understand it correctly).

  4. If you developed a third party GPL script for a site that someone else licensed under GPL, what would you have to do exactly for both a server-side script and a client side script? What does static and dynamic linking mean?