I guess faster loading could be it? But generally it’s more of a layout problem than a bandwidth one.

There was a website which I allowed ads on to help support them. One day, I went to that site in my browser and my laptop fans spun up at that time. Turns out that ads on that site caused my processor usage to spike near 100%. A reload fixed the issue. Once that same thing happened 2 to 3 more times, I just blocked all ads on that site from then on.

There are times that people can't throw the resources of an Intel i5 processor towards rendering the advertisements on one website. I would think that is more common these days with Chromebooks running the modern equivalent of a Celeron processor. Phones also don't have much processing power to give and will warm up and drain batteries all towards the all important goal of "render those advertisements".

I think people tend to allow advertising until it becomes a major problem that needs resolved (such as if the site is bogging down your computer or if the advertising makes the site unable to be read easily). Since those people would then need to fix the issue and hopefully fix it for good, it is easy and efficient to just block out all advertising forever.