I remember when I got into affiliate marketing, one of the things that really confused me a lot is WTF is a postback URL, what does it do, what is a SUBID, why do we need it. What is a tracking pixel.
I am now training some new employee of mine, and made a diagram in mindjet to easily explain it. Here it is, hope it helps.
To put it simply; if you don’t place the postback URL or tracking pixel; then your tracker won’t be able to tell you if there was a conversion or not. That is why you need to use it.