As you know the usage of JavaScript has been more and more used in web applications over the past years for technologies such as AJAX. JavaScript can accomplish really cool stuff on the client side and make the user interface more interactive and responsive. Just take a look at SharePoint 2010 - that’s some heavy JavaScripts there (a bit to heavy IMHO).
So lets assume that you are building some new cool stuff, in SharePoint of course, and why not a Page Component for a contextual Web Part. That’s a lot of JavaScript (apart from the server side XML chunks)! So now you are making your web page payload even heavier. This is when minifying comes in. Minifying is a way to minimize the payload of a resource such as removing unnecessary comments and whitespace, shortening function and variable names etc - all to make the payload as small as possible. The only problem with these minified scripts are that they are virtually impossible to debug (and believe me if you are building a Page Component for SharePoint - you need to debug).