I gather that it had a use unrelated to Lemmy but for Lemmy posts I make a case here that it is more misleading than helpful. For a moment, please ignore the underlying reasons why things are the way they are and focus on how the issue presents to the end-users.
(1) By pulling in solely the post, but not any of the comments, it at best provides only partial information - which if all you wanted to read was the post, then why bother pulling it here at all? (as opposed to retrieving from its original location - I mean, to do it you already need the full URL...) While if instead you wanted all of the comments... - e.g. to be able to reply to - then too bad, b/c it won't do that?
(2) It also does not pull in any of the old vote counts. So if hypothetically a post had 1000 upvotes, and then after pulling it here it received adjustments +2 from upvotes and -4 from downvotes, then its total would then be 998, right? Except PieFed would instead display "-2", a qualitatively different score for a highly popular post that is a terrible misrepresentation of the actual facts about it.
(3) It conveys a distorted view of things to the end-users. e.g. see [email protected] where there are 6 posts from the last 2 months, right? Right?! No, there is actually only a single post there in its entirety, then a few more that I and what I assume was Blaze pulled in - note how those other 5 have zero comments, and total scores near zero, due to the aforementioned issues. Really the "earliest" post that PieFed.social reliably has from that community is from 4 days ago, and then beyond that is a scattered, partial mess. There are actually MANY more posts from the last two months, which are not represented here. Ergo, the initial impression that a quick glance at this community offers turns out to be false, due to these federation issues.
(4) showing only partial information is often called a "false positive" or type I style of error, whereas showing nothing at all for those posts that are not fully here avoids that pitfall. If certain content is not here then... well it is not here, and that's that, but for only some of it to be here leads to much confusion, imho.
Almost entirely distinct from this issue, the ability to find an existing post given its URL should be added to the search menu, b/c that is where people will go to find it. But ofc all the more so if the retrieval button is removed or made less prominent, so that that find ability is not lost along with that.
I understand that there are hard limitations of the federated model itself. So if e.g. older comments and votes cannot retroactively be pulled in - or possibly even if so - then maybe this function should just be abolished? Or perhaps a couple more layers of "are you sure you want to do this?" added, or better yet moving it from its prominent place showing up to everyone on almost every page to a more subdued location where only those who know what it is and what will happen if it is used are likely to access it? I now feel that I actively made the situation in [email protected] worse by pulling in those posts, and wished now that I hadn't done so, as it could lead people astray into thinking "this is all the posts that the community has to offer from this time-period" (NO, it actually has MANY MANY more than that, on the original server!?!!). Now that I know this I can refrain from using it, but it would be nice to help others who climb this ladder after me as well:-). So I am sharing my thoughts with you in case that helps.
PieFed is freaking awesome and you all who work on it are magnificently extraordinary to share your knowledge with the world:-).
Ofc, there's an xkcd for that:-)