I had two papers come back with rejections last week. One had been under review for something like nine months; I submitted the other one the first week of July. One came back with two sets of relatively extensive comments; the other came back with literally no explanation whatsoever. It should come as no surprise that the fast decision was the explanation-free decision. This journal told me that they aim to make these decisions quickly, and that this makes it impossible for them to explain the reasons for the decision. But while I appreciate a swift decision as much as anybody, this is the third paper I've sent them in the last four years or so, and it's never taken them longer than eight days to come back with a rejection. That makes me wonder what editorial procedures they follow.
The other one was rejected for what I think are decent reasons. While I think (in my unbiased opinion) that an R&R might also have been appropriate given the stated reasons, it is clear that the paper should not be published in its present form. (Also, this wasn't surprising--there were several times during the wait that I found myself wishing for another an opportunity to revise the paper.) And I am grateful to this journal for a) putting me in a position to know that the reasons were good by sharing them with me; b) putting me in a position to change the paper in response to the criticisms by sharing them with me, and in so doing, to use this experience in a positive way.
I don't really have a larger point, other than that I wish it was more common to get helpful feedback with rejections, and that it was more common to get a decision in under six months (I really wish it were four, but let's not get carried away here).