They get stronger (as above) with fewer people at the table. Also if you're short stacked. Barring those situations, I don't think you lose much letting 'em go, especially EP.

In late with early folders and a mid caller or two, they're raisable. If the flop touches one of 'em you're pretty much required to bet big and drive off the Ax guys. If called on the flop, I think you bite the bullet and check it down if you can.