Some filter addons perform complex logic trees based on properties other than the hostname(s) being loaded by the browser, and therefore take up more CPU and RA

Some filter addons perform complex logic trees based on properties other than the hostname(s) being loaded by the browser, and therefore take up more CPU and RAM for more wall-clock seconds to meet the needs of their increased complexity. They end up able to block more content than others, but that comes at a cost — which, as this page notes, can be much higher than anyone expected.