Love Ublock, But out of Curiosity, what stress did purging cache actually cause?

I really know nothing about how Ublock works as a program, I am amazed constantly by the sheer amount of work that gets put into this, I came as a recommendation from a friend back when the funny red play button site was doing its thing, and I wish I knew about this way, way sooner.

However, due to me not being exactly program or tech savvy, Ever since this update, which I like, I saw that the purge cache button was remove because it caused unwanted stress. So out of curiosity, I ask what kind of stress? Was it to their servers? To Programmers? To computers? All of the above? Nothing against removing it, I just am genuinely curious as to what kind of stress that button was causing