In game that are large or bigger I find the crap planets (pq 3-7/8 ish) to be rather worthless due to the amount of development that can happen on them. infact they often are never able to break even economically (or atleast develope in a timly maner) generally speaking I avoid these planets at all costs. however the problem is that the AI eventualy will take them.
Later on when war breaks out between me and some other AI ; the AI will have some number of crap planets for me to invade. as I invade and conquer these colonys it would be great if when I abandoned them I was asked weather or not Id like to make the world uninhabitable for anyone else. this way im not playing host to crap planets who just suck resources and yet at the same time doesnt create more worlds ill have to invade later.