You know your site is fast in Mountain View, where you have fibre and sit 100 feet away from the servers, but most of your users aren't in Mountain View. Most of them aren't in the US! Google's PageSpeed results are great, but they're not going to tell you how fast your page loads in Uganda or Australia.
Folding a Where's It Up
fast test into your monitoring suite
can help you keep tabs on the new global market. Rather than
reassuring yourself that if it's fast at home, it's probably
fast elsewhere, you can monitor page load speed from fifty
locations every fifteen minutes, keeping your metrics
international, and your page speed obsession well-fed.
Load a website, and return load-time details for each resource on the page.
Download a large file, and return detailed timing data.