One thing to remember is that not everything makes a good aspect. Sure, you could roll fists to give someone the aspect "pinned", but then what? If you don't follow this up with a grapple, the aspect will probably be gone as soon as do something again, unless that something is making sure the other guy is still "pinned". Fights are messy and quick.
Then again, there's "invoke for effect", which lets you do all kinds of cool things. Though I have to admit, I forget to utilize it far too often myself. It basically lets you enforce the truth about an aspect. Doesn't always have to be done as a compel, though it might, if it is a game changer.
So for instance, "pinned" doesn't really do much. But you could say that you are tipping over a bookshelf and as luck has it, it falls on one of your opponents. He's now got the "pinned under a bookshelf" aspect on himself. Now in itself, it doesn't do that much, because you can only invoke it for a +2 on something. But he's lying under a bleepin' bookshelf, he's not going to be doing all that much for now. To enforce that you can use your free tag to invoke the aspect for effect. The GM decides that the bookshelf isn't too heavy, so getting free of it would be a difficulty of 2 on a might roll. The trapped character can do other things, as long as it makes sense for him to do them buried under a bookshelf. But he would need to take an action to free himself from the bookshelf before doing much else.
"Invoke for effect" is really your goto method of doing anything messy with aspects, anything that doesn't really fit into the rest. Often times, these effects can also be ground zero for a round of mass compels. For example, you invoke the crack in the only supporting column of the cavern to say that it breaks and now everyone inside is more concerned with getting their hide to safety rather than keeping hitting each other. You could, of course, buy out of the compel, saying that while you run out, you keep a clear enough head to keep shooting the bad guys to make it harder for them to escape the cave in.
These things can often be used to completely or partially rewrite a scene. Like the example above, it goes from a fight in a cave to the escape from the cave.