Speedtest.net helps you to know how much bandwidth your connection has. This can be very important information if you are having connection problems. While the problem may be with a specific site it could be some line issue. The line could have problems or someone down the hall is downloading a multi-gig movie file. One of the things I like about Speedtest is that it can keep a history of your bandwidth tests. Seeing a pattern might help you to figure out what is going on.
If you're like me and have an international audience for your web servers, being able to know the effective bandwidth to various parts of the world is very useful. It's the only way to measure the experience your overseas users are having. This is critical if your distance-learning program has students in multiple countries.
I've been using various speed tests for many years and this one is by far the best I've used. Highly recommend.