What role does the "mission" have in sandbox play?
By mission I mean an in-game objective which the characters seek to achieve, arising out of their own motives or due to their taking on a task given to them by another. I'll give a few examples to show what I mean:
1. In the brief Stonehell Dungeon game I ran, the party captured some goblins trying to sneak out of Stonehell. They learned of the goblins' conflict against the orcs and decided to help the goblins out, mainly so they could use the goblins as fodder against the stronger orcs. The mission: eradicate the orcs on the first level of Stonehell. (Voluntary, wholly player driven).
2. In the lengthy and fun 2E game in which I played while I was in grad school, our party had some downtime in a big city during a festival. During that time, we were approached by a few different sorts of people, each of which wanted us to do, find, or recover something and get some sort of reward in return. We elected to help this magic-user named Rinver travel to a ruined temple of Oghma in exchange for payment and a big share of any treasure. The mission: get the magic-user safely into the ruined temple. (Voluntary, somewhat player driven. That is, we were given a choice of missions and took one instead of just saying "let's see what's in this hex over there").
3. In the same game, my character became cursed. Well, it was mostly his own fault, but that's another story. The point was, to remove his curse he had to travel to the distant desert of his youth and recover an artifact. The mission: travel to the distant desert land and recover an artifact. (Involuntary -- my character would have Bad Things happen unless he did this thing. Not very player driven -- the curse was a consequence of my PC's actions, but the manner of the curse and its removal was not).
I'd submit that the mission has a vital role in sandbox/old-school play. I believe all three types listed above can fit, if posed properly. Missions that are offered as actual choices and/or consequences of PC's actions can fit quite well. In #2, we could have turned down Rinver and accepted an alternative offer. In #3, while I did not know my PC's actions would lead directly to a curse that would then necessitate a mission, I had a good idea that Bad Things could happen by continuing on the present path, yet I persisted. The problem comes when missions are presented as meta-game imperatives, as in "You have to take this wizard's offer or we have no adventure tonight."
Thoughts? Does the mission have a place in sandbox play?