When comment threads get long, the system raises an automatic flag. One of the options from the moderator UI is a button, "move comments to chat". This creates the chat room and copies the comments but doesn't purge them. That's how "move comments to chat" used to work everywhere.
There is also an entry on the moderator menu on a post for "move comments to chat". Recently this menu option was changed to add a checkbox for "also purge the comments", to much moderator rejoicing. Now, instead of (0) read through comments, (1) move to chat, (2) purge all comments, (3) show deleted comments, (4) undelete the one with the link to chat, after reading the comments we can do it all in one step. That's great!
Except if we're handling this kind of flag, the sequence is: (1) see flag, (2) read through comments, (3) scroll back up to the post menu (which is above 20+ comments), (4) move, (5) dismiss flag. It sure would be nice if the "move to chat" button available in the flag UI offered the same purge option that the mod menu does. That would reduce the process down to: (1) read, (2) click the "move" button, (3) check "and purge".
(You might even consider checking that box by default; when do moderators not want to purge comments that were problematic enough that they chose to send them to chat?)
It's not a lot of clicks, but it's not just clicks -- there's all the scrolling (or paging) to get to the menu from the end of the comments. Sure, all this only adds several seconds; it's not a major hindrance. But it's a minor one and it seems like it wouldn't be hard to improve.