InstanceNotes

InstanceNotes helps you remember your important notes about each dungeon: Mythic+ enemy forces breakpoints, talent choices, common Bloodlust points, route reminders, boss notes, skip warnings, or any other details you want to see at glance next time you are in this dungeon.

When you enter an instance, your saved note appears automatically in a simple on-screen panel, so the information is visible without opening extra menus.

You can create and edit notes per dungeon, making it easy to keep different reminders for different instances.

There's also an option to post the current instance note to chat - only for you or for party - by pressing hotkey, if you don't want note panel to be always on screen.

I mostly use it to save important enemy forces breakpoints for Mythic+ dungeons.
For example:
Pit of Saron - “78.38% before going up”