As a writer, I like to hear what someone likes and what they think is lacking. Although, I keep in mind that some readers are looking for an action-packed rollercoaster ride while others prefer a long, drawn out drama. Some people prefer simplified descriptions while others prefer a verbose depiction of every minute detail.
When a reader takes the time to review, they are letting the writer know that they've read the story and thought it was good enough, or bad enough, to merit comment. I'm usually satisfied with "Brilliant!". I don't mind a good, old, "That was great! Looking forward to more." My favorite reviews point out something in particular, something that struck them as odd, something they want to see more of, something they particularly liked. All in all, I'm not terribly picky.
The pros of asking for detailed reviews would certainly be the added input or concrit the writer receives. If the writer thinks they have a pacing issue or they’re not sure if the flashback scene works as well as they hoped then they should mention it in the a/n. Then the reader will pay more attention to the part, and while they’re reading, make mental notes about what worked, what didn’t, and ways to improve the problem or dispel the writer’s worry about that point.
The only drawback I see is that some reviewers who might leave the one line reviews might pass on leaving a review in that case. Some readers might think the writer seeks more comment than they are either prepared or feel qualified to provide. I’ve heard from several regular reader/reviewers that they simply enjoy the stories. They aren’t wrapped up in grammar/tense/formatting/pacing/continuation/etc. In that case, perhaps a note saying, “All reviews welcome…” or something to that effect that would prevent putting any distance between the writer and the “pleasure reader”. Those one line reviews of encouragement are equally, if not more important to me. The more of those I get, the more people I know are reading the story…and actually enjoying it.