When I'm looking for an image, I expect my search engine to return me a URL with .png or .jpg at the end of it.
https://addons.mozilla.org/en-US/firefox/addon/dont-track-me...
Depending on some conditions that aren't always you get the true link or you get the wrapped link.
My guess is that they have an array of techniques for tracking your clicks (js trickery, "ping" attribute,...) and resort to wrapping only when the other ones are less likely to work.
Example (Chrome):
<a href="https://developer.mozilla.org/en/docs/Web/HTML/Element/a" ping="/url?sa=t&source=web&rct=j&url=https://developer.mozilla.org/en/docs/Web/HTML/Element/a&ved=2ahUKEwjmxMHk5MvlAhWVvp4KHS6lCqIQFjAAegQIABAB">Before, all the results generated were direct links without any wrappers. Then Google decided they needed to know which of the links people were clicking so they injected a wrapper around every link so they'd get a request from every click.
Sure, it can be used to increase accuracy of search results. It can also be used to taylor data and profiles around individual users at finer and finer granularity.
The first few results from the searches all have recent "Doesn't work anymore"-ish comments.
The first one works for me.