A thread with forty messages is not a reading problem, it is a search problem — and the thing hardest to find in it is what you failed to do. Your own obligations are scattered across other people's paragraphs, usually in the second half of a message whose first half was about something else. Ask for a summary and you get a chronological account, which is the least useful possible shape: it tells you how the thread developed when what you need is what is outstanding.
The section that earns this prompt its place is the second one. Unanswered questions are almost invisible from the inside, because you remember the message arriving and you remember thinking about it, and neither of those is a reply. Having the thread checked message by message for questions directed at you, against replies you actually sent, surfaces things that have been quietly pending for weeks.