Reporting each and every post is like making twenty to thirty 'threads' in the report queue. If a thread is derailing, make one report where the derail starts and then give extra details from there in that report. For example, if there's a twenty page thread, and every post after page fifteen is a derail, you can say "A major derail started from this reported post here, and has gone on from here to page 20 in the thread". That tells staff where it started and where it ended.
If there's other details, you can add in more though to let staff deal with it quickly, as well as check to make sure the report is accurate. For example, a post like this tells staff everything they need to know quickly. "A major derail started from this reported post here, and has gone on from the post here on page 15 all the way to page 20 in the thread. That said, Jimbob has been the biggest spammer, the author Alice has been trying to get people to stop shitting up the thread, and page 18 the users Bob and Aerith tried to get things back on topic before the users Jimbob and PrettyPrincess came back and messed everything up again".
See the difference?