Short URL Hints
It looks nicer. The masking URL certainly looks a great deal prettier than the ugly ClickBank link it replaces.
It's shorter. Affiliate links can be so long that they wrap around to take up more than one line on your webpage. This may be disastrous in the event the link is broken in order that clicking on it only puts the very first line in the browser address bar. That will certainly cause a FILE NOT FOUND error, so your prospective customer gives up in exasperation.
It looks less like an affiliate link. In our example above, the original link is a bit obvious. Some ornery people just can not stand the idea that someone they don't even know is making money from their purchase, even though they do not save any money by not using your link.
It looks less hazardous. Some nervous nellies won't click the link at all because they are worried about viruses, phishing, porn, etc. Cloaking affiliate links makes the URL appear like it's really a page on your webpage, so they feel more reliable in clicking on it.
Google dislikes affiliate links. It really is against their "guidelines" for a site to exist for the primary purpose of selling another person's product. If they receive a complaint, or otherwise assume that your web site violates this policy, also they can de-index you - in other words, your pages will not be listed in their search engine results!
It's simpler to modify. There can come a time when the product you're promoting is suddenly moved to an alternative page on the affiliate site. If this happens, your cloaking link needs to be changed in just one place - it's cloaking page. It's masking URL need not be changed on every page where it appears on your web page.
Link piracy is less likely. This really is probably the most important reason for masking links. An unscrupulous internet marketer may see your affiliate link, and substitute his own affiliate Short Link for yours. Then he will acquire the product at a discount - and also you lose your commission.