What is a Tracking ID? When should I add it to my hoplinks?

You can add a tracking ID to the end of your hoplink. In this way you can find out the sources of your sales.

For example, you have a hoplink that promotes a vendor 'ABCDE'. It looks like:
http://yourid.abcde.hop.clickbank.net/

Let's say you paste this link to your blog giving it a tracking Id 'blog' and to your forum signature giving it another tracking Id 'forum':
http://yourid.abcde.hop.clickbank.net/?tid=blog
http://yourid.abcde.hop.clickbank.net/?tid=forum

After a while, in your ClickBank account, you can check how these two different sources perform: which one gives you more sales, which one has a larger conversion rate, etc.

As well, you can use Tracking IDs to split-test different versions of your presale pages (or ads, articles, videos and so on).

Notice 1: The Tracking IDs can be up to 24 characters long, and must consist only of numbers and/or letters (no punctuation or other symbols).
Notice 2: If you have an encoded (with the HopLink Shield) hoplink, you don't have to re-encode it for each new tracking ID, just modify the '?tid=' part.