Many times there are code samples on Github that have simple static files that you would want to run on a server, such as the case if there are ajax calls in javascript files.
Sprites are often used to stylize 'a' tags. When a sprite sheet is used, a fixed width and height is used to specific the image on the sprite.
Most of the time, css rules are overridden to get a different style, but some rules need to be outright removed. For example, if a hover effect is in place when javascript is disabled, but the rule might interfere with the javascript code when javascript is enabled. This might happen when using a jQuery plugin for menu creation or text effect.
// Visibility Test Cases
$("#word").is(":visible");
$("#word:visible").length == 1;
$("#word:visible").length > 0;
$("#word").css("display") == "block";
$("#word").is(":not(:hidden)");
!$("#word").is(":hidden");
Older versions of jQuery are still being used (<= 1.6), and those versions do not support the new "on" method of attaching event handlers to elements. If you were authoring jQuery plugins and want to ensure compatibility when working with events, then you would want to write an adapter inside your plugin.
If the styles of stylesheets are atrocious, and you have no control over its loading, you may want to disable specific stylesheets with javascript.
Use event namespacing when attaching or detaching event listeners. This reduces the possibility of you accidentally removing event listeners that was not intended to be removed. This is especially important if you plan to use someone else's JQuery plugin that interacts with an element which you are also manipulating through your own event handler attachment or detachment. There could also be the opposite problem where someone else's JQuery plugin removes your attached listeners. This is why namespacing events is a good practice.