Last week sometime, I started writing-up a "policy document" which I had planned to re-top and post to the current timeline and link from the "join" post. Unfortunately, I got distracted and it's sitting in my drafts, but because shared comments have come up twice today...
As far as I'm concerned, it is preferable for a shared comment to have enough info before the jump that someone should be able to judge whether it's worth clicking-through. Whenever I write a comment with the intention of sharing it to a community, I try to squeeze in as much before the jump as possible and often I will phrase it so that the entire comment will be displayed. I also use this as a measure for comments from others which I share. Though I don't have any control over their wording, I prefer comments which are full or at least has more than one non-specific line displayed. If we were on one of the ad-supported blogs and if a paid blogger were to post only "this is cute" or "important info" without a mouseoverable link, they would be lambasted in the comments. Sometimes it may be unavoidable, but I'd rather someone write and share their own comment in response to one lacking the necessary info than to post something a person would have to click to know what it's about.
Also, I understand that another community has had some drama regarding unshares and they've adopted a policy discouraging it. This is not the case for Crosstalk. Because one author thinks everyone should see or care about something, it doesn't mean that we all have to agree and just as we each have the right to share, we also have the right to unshare. Of course before someone unshares something, they should think about how they'd like their shares to be treated and if someone decides to reshare, they should think about whether they'd like their unshares undone. Just as there is no rule governing what can be shared beyond our normal content guidelines and the Kinja Terms, there is also no rule for unshares. As authors, it is up to us to curate this space and let there be no doubt, I both share and unshare. Though I'm hoping you use similar and consistent criteria, I expect others to do the same.
Only somewhat related, but worth mentioning: we've long had a rule about calling out other commenters and unpaid authors by name or pointing toward someone's comment with just a couple of disparaging lines and a link. I understand this may be more acceptable elsewhere, but it's not the reputation I'd like to cultivate for Crosstalk. Instead, if there is a commenter on one of the mainpages with whom you'd like to disagree, I'd rather you formulate an argument and not use their name in the top-post. One workaround for this would be that you could directly share their root comment or a reply because they should be able to stand behind their own words, but the shared comment should not use offensive language or an NSFW image before the jump and you should understand that any other author can unshare it at any time.
And finally, I should add that if I spot a battle of wills over a share, I'm most likely going to lean toward the unshare. Of course that may not always be the case, but I really can't see many circumstances when it would be important for a comment to be shared. I don't feel we should be sharing things just for the sake of an argument, but because they are like mini-posts.