Over the last year or so the Drupal projects I have been involved with at work have required the need to work with a lot of video files being maintained in Drupal. Well, as you can imagine the larger the files we are maintaining the greater the strain this puts on our host to serve the files. To try and account for this we moved as many of the assets in Drupal as we could off to a Rackspace Cloud Files account so they could be served from a cloud delivery network.
If you have spent any time writing Object Oriented PHP or Drupal PHP you will know that there are many instances where it can be handy to know exactly what you are dealing with at a specific point in your code. For example, possibly you are troubleshooting an issue and cannot figure out why a variable is not acting as it should, or maybe you are writing logging routines to make sure all of your exceptions are logged for future troubleshooting. Whatever your needs may be it can be very helpful to use PHP Magic constants to assist you in your troubleshooting.