Based on
http://www.jimbutcheronline.com/bb/index.php/topic,24061.msg1022205.html#msg1022205From a mechanics standpoint, there seems to be a deliberate disconnect between the invocation (which can be an invoke-for-effect that in turn triggers a compel) and the compel itself that results. So this makes me wonder if the interpretation should be as follows.
When you invoke an aspect for effect, it has the relevant effect on whatever scope is appropriate. So a aspect placed on an individual would affect only the individual, while an aspect placed on a scene would affect the scene. If the 'effect' in question is intended to cause trouble, then this effect would then basically act as a bribe to cause the GM to issue a compel against any involved individuals.
So if the scene has an aspect of "Strong Gusts of Wind", then you are allowing two things to occur:
1) If the GM feels it's appropriate, he can offer a compel to anyone or everyone in the area (and should probably lean toward everyone), and those who accept the compel will be troubled in some negotiated way. Perhaps they are knocked down, for example.
2) If a player chooses to, then they can spend a Fate to invoke the aspect for effect, which then triggers #1. The player is paying one Fate to make the aspect cause trouble to the scene, and that trouble is resolved as a compel against each individual in the scene (with Fate coming from the supply).
One thing to note, by the way, is that there does not seem to be a mechanic for casting a spell to place an aspect on a zone. An attack can be against a zone, but a maneuver places an aspect on an indivudual or on the scene (which means that an invoke would cause trouble for everyone on both sides, rather than being focused on the group of baddies in that zone over there). This is probably a good thing; it makes the above interpretation more balanced.
Note also, of course, that the compels can still be bought out of as normal. Ex: As the GM distributes the Fate to all and sundry after the wind kicks up, a player might refuse the Fate, toss in one of his own, and say that since he was up against a wall at the time, the wind had little detrimental impact on him.