You can only pickup the thing once to finish the quest. So it's not like you can sit and gather a ton of the things to sell or otherwise profit from, it jsut means that there isn't a line at popular quests where you have to wait, and wait, and wait for the items to respawn.
Not OP and not sure of the quest name, but Ally side, one of the early quests you get in northrend as soon as you get off the beach where there's the small village /farm with ghouls and mechs and mine. There's a quest there where you have to pick up a red book in the burning house, last time i did it (2 months back) the respawn was literally 14 minutes and i was competing with 3 others. gg to those guys, but this one's brutal.