If you want to receive a short URL which will work only limited time, you may check this box.
When user click on previewable link he can view the long URL first.
RLU.ru — is a short URL service. With the help of RLU.RU you can transform a long URL info into a short one. The short URL will only have a few symbols.
The RLU.ru service is very useful in such cases: when you have a restriction for a number of symbols; when you can’t afford to use a long URL in a text.
For example, using RLU.ru let you shorten any URL on «TWITTER» or in a «Text Message». Usually those have a restriction for number of symbols.