It is at best neutral for the user. Sometimes these source trackers help companies know that affiliate links are more often drivers of traffic. Other times it helps with A/B testing because they discover the main logo was more often clicked than the "click me" button or whatever.

But how does this help me as a user?

Affiliate links are often hidden, and depending on the system might even lead to higher prices, because the shop is offsetting the affiliate program cost.

Whether the company does A/B testing, what does that have to do with me? That also can be implemented without external trackers and just be set in a session.

So I would say it’s a net-positive.

Cash back portals often require click through on affiliate links.