We really love open source here in Wedia, and jQuery is the open source Javascipt library we prefer. A very common task we perform, specially on large scale sites, is to check if an element exists on a specific document (page) before doing something with it. Sure, jQuery is not throwing any errors or warnings, although the Javascript code runs without any particular reason and as a result we enforce the browser to waste valuable resources for nothing. In large scale sites this issue can really slow things down.