What is a URL?
Think of the internet as a really big neighborhood. The wires that connect the servers to computers are the roadways, each individual website is a house and the URL (Universal Resource Locator) is the address for the website.
Why would a URL need to be shortened?
URL's can be extremely lengthy, containing long strings of characters. It can be highly beneficial to shorten URL's for a number of reasons. Shortening a URL helps cut down on the character count of a text message. Since a single text message is 160 segments, text message real estate is at a premium. Shortening a URL will free up additional character space for you to convey your message.
Cell phone providers are very vigilant when protecting their customers from spam texts. A text message containing a long URL might indicate to the provider that a spam text is being sent and they will subsequently block the text from being delivered. Having a shortened URL is much more efficient and is far less likely to be flagged as spam by a provider.