selenium-referer - An example of adding a Referer request header in Selenium tests with Python and WebDriver
Sometimes, websites need to have different behavior for cases when users come from different sources / search engines. In my use case, our website had to set a tracking cookie which would have different values for users that came grom Google, AOL, Yahoo, or MSN. I had to test that the cookie was being set correctly for all cases. First of these options requires manual intervention from the user, so it's harder to distribute it. You have to explain to the person who's going to be running the tests how to do all this, as opposed to just installing the needed packages and running with it.