It works better when characters have the same purpose, whatever the underlying motive. An aged paladin found himself dying in a small town and found that there were half a dozen youngsters determined to take up the adventuring life, but having no more aim than that. He shows them the magical objects of years of adventuring, but warns them that with them comes the task of finding undead spirits that are not evil, discovering why they can not rest in peace, and completing the task.
But that's limiting, both in character and plot.
On the other hand, two characters, one of whom wants to complete quests that will allow ghosts to rest in peace, and one of whom wants to avenge himself on a villain, pull the story apart. In order for it to work, both characters would need some limiter. Perhaps both the revenge and the quests need research, so they trade off knowledge if they find any, and the would-be avenger joins in the ghost-laying quests for purposes of level-grinding to ensure he can deal with the villain when they meet. And that's just two characters! For the others to just want fame and fortune, or a life away from their homes, or other non-plot-generating purposes may be necessary to keep the story in line.