Anyone doing the crafting/gathering class quests (which for gatherers at least you should, as skills and traits are locked behind them) should do it before 80 because they give a huge amount of experience. Doing one crafting/gathering job's 60-70 quests nets you about 40 million exp, for example.
There are quicker ways to get that exp, but if you're gonna do them anyway, might as well do it and not waste more exp than you'd need for even level 79-80