Does writing something in the chatbox under a report even do anything?

in case a human review happens (lol gl on that one) your comment may be usefull. tbh i have no idea how many manual reviews happen on a daily basis so i cant say much, but i seriously dont feel like writing anything into the reports unless its someone who trolls in a special way that you might not directly see.

The system is not entirely automated, it goes to a human employee for review in some cases.

Anything above a chat restriction has to be reviewed.

For automated punishments, it likely doesn't do much. However, in the event of manual reviews, I feel like they play a much larger role.

Although, if a person was reported multiple times with the note "Post game" or "Pre-game" and referenced chat, I'd think the automated system may play a role there. Just conjecture, I suppose.

It's not entirely automated, but I don't know for sure how much descriptions help. I always leave a description, but quite frankly, I don't know if it helps or not. I'm surprised there's so many posts here, but not one from Riot. Was hoping they would give a definitive answer.

Before the IFS, I would take screen shots because player support previously couldn't see pre-game or post-game chat and I would host it on some site like imgur or something and post the link for the box. Now that IFS scans all of it, for chat related offenses, I don't bother any explanations. I just check off the appropriate boxes and report and move on.

Now for gameplay reports like inting or trolling, I do type it to point out certain time frames or descriptions of events where I distinctly remember toxic gameplay behavior so that player behavior specialists can take a good look at specific times and try to find a better way to detect the troll behavior.

I honestly have no idea if player behavior specialists do read the comments, but I do it anyway just in case they do.

a lot of reports get manually reviewed if they are reported by multiple people but the system doesn't get tripped, so yes

Yes. Sometimes a report is borderline punishable. Comments help if a manual review is needed.