The benefits of a URL Rewriter have been explained many times, by many people, so I am not going to add just another rant to the web about keeping your URL’s clean for the search engines. I will just leave you with Jeff’s explanation of why you shouldn’t ignore the URL. Having multiple URLs reference the same content is undesirable not only from a sanity check DRY perspective, but also because it lowers your PageRank. PageRank is calculated per-URL. If 50% of your incoming backlinks use one URL, and 50% use a different URL, you aren’t getting the full PageRank benefit of those backlinks. The link juice is watered down and divvied up between the two different URLs instead of being concentrated into one of them. While Jeff only focuses on the reasons related to SEO, there are many other reasons to make your URL’s “look-and-feel” a hire priority. One that is often touted as a wonderful reason to use a URL Rewriter is to produce pretty looking URL’s, and even though this one of many reasons to use a rewriter, it is really a small part of why you want to have a URL Rewriter in your arsenal as a web developer. Other reasons include forcing your domain to a constant www vs non-www address, having helper URL’s such as http://www.microsoft.com/sql that redirect to their actual location, and many others.