It is not TOTALLY useless. If you get a small number of miles in a programme because you take a flight on an airline you would never ever normally use, you can usually convert them to something you can use. Yes, the rate is terrible (my 1000 US miles got me 100 Priority Club points!) but that is 100 PC points more than I would otherwise have had ....
(And I got some PC bonus points during a 'use our partners' promo!)