At least these 3:
- You can read threads in ignored boards (e.g. somewhere else in the forum you find a link to a thread in an ignored board), however you can't post there. Sometimes it's useful and/or interesting, and you may want to keep that thread open in a tab to monitor it, but not being able to post is a downer. Temporarily unignoring the board just to post is too much work, and permanently unignoring the board pollutes the "Show unread posts since last visit".
Can probably live with that limitation.
- "Show the lasts posts of this person" (in a user's profile page) doesn't show posts in ignored boards so you don't get the full picture.
That is pretty bad (especially if people doing that to spot possible scammers) although I rarely actually use this function (so can probably also with live that).
- "Show new replies to your posts" doesn't show new replies to your posts in ignored boards.
I don't use that useless link except if I click it by mistake (I use Watchlist) so I think I'm "good to go".
Thanks for the help.