Apart from the reasons he mentioned. Here are two more to consider.
More Referrer DataHave you ever looked at your stats and seen a bunch of blank referrers? There are multiple reasons why this can happen, for example it could be a bot acting like a browser ora user with some sort of privacy protection add-on. But sometimes it's because the referring URL is secured via SSL.
Browsers automatically strip out the referrer info when from from https->http. Which means that if your redirect link is not secured the referrer info will not be available to Prosper202.
This also means that you can use this same fact to...