The media upload functionality in Sitecore only handles direct file upload while you sometimes would like to add a media item from the Internet. There are for example Digital Asset Management (DAM) systems that use URL cut and pasting as a means of integration.
The drawbacks of this method of integration is that the web site will depend on the media being available from the DAM system which it may not always be. If for example the DAM is down a single point of failure is introduced in the web site. If the editors remove an image from the DAM system they will have no way of knowing that an image actually is used in a web site. I personally do not think that URL cutting and pasting is a good way of integrating a DAM system, but sometimes you have to deal with the systems already out there. Continue reading A very simple media upload via URL