Well there are situations where intrusive list pointers don't work well. If you don't control the class, then you simply can't put pointers in it. If most objec

Well there are situations where intrusive list pointers don't work well. If you don't control the class, then you simply can't put pointers in it. If most objects aren't ever in a list (eg. a million objects but only ten in a list at any given time), then you're wasting space. If you want to put objects in several different lists, then you have to know up front how many lists and their names, and this can become unmanageable.