Every once in a while, someone posts a question that relies on an image or a Wolfram|Alpha link with a formula or the like. In the case of images, it's often because they don't have sufficient privileges to include the image, and then someone soon includes it for them. In the case of formulas, it's probably because they want to save the effort of typing the formula out in $\TeX$ when you can already see it nicely typeset by following the link.
It usually doesn't take long before someone else comes along and edits the question to make it self-contained and/or asks the OP to do so or to please make questions self-contained in the future. Today one user asked three questions containing W|A links and no formulas (1, 2, 3) and at first didn't react to my comments about the questions not being self-contained. On the third try, however, he or she did react, saying that it seems redundant, and immediately got an upvote for the comment. I can see why it might seem redundant. Since I haven't seen any discussion of this policy and couldn't find anything about it in the FAQ (e.g. here), I'd like to find out how people think about this, whether it's just something that a few active commenters care about or a policy that's in place for a good reason.
The main reason I see for this policy is that questions and answers are meant to persist and be useful for people who find them later, and we have no control over what other sites do to their URLs or even perhaps their continued existence. Some also emphasize in comments that it's annoying to have to click through to another page, but to me that's secondary; if it would save the OP a lot of typing, I wouldn't mind clicking through to another page. I'd like to hear your thoughts on this (in particular further reasons you may see for this policy), and to get an impression whether there's a broad consensus on this, since I think it only makes sense to ask people to adhere to it if there is.