I broke it down into this:
GO AGGRO: is threatening someone with violence, blackmail, brutality, or leaving the threat entirely unsaid but understood. To threaten them with violence is an entirely different matter then promising them violence. If you aren't going to pistol whip the fucker if he doesn't play along, then you're not being hard enough for this move. When the character will do something bad to someone unless... its going aggro. On a partial hit, if they don't cave, you actually do try to good on your threat, but, you hesitated, flinched, were distracted, or just a hair too slow to pull it off. You don't deliver, they dont either, but they're forced into one of those other choices. We actually used this a few times for political moves were the go aggro acted on a larger time scale of an entire day where someone attempted to blackmail a hardholder.
SEIZE BY FORCE: is when you want to inflict harm or seize ground, there are many situations where this comes into play. I always try to tell people that "take definite hold of it" is the tactics. So if you wanted to bash a guy with a gun, taking definitely hold doesnt mean you definitely made contact, hitting meant that. Taking definite hold might be you hit them and cut off their escape, or knocked something out of their hands, or forced them out of their position. etc.
The thing is, if the guy wasnt ready to avoid the attack, or would cave no matter what, you dont have to ask your players to roll. They just do it. If that guy was sitting down and you pulled out your gun and thee was -no chance- for him ot notice something was amiss, or otherwise could not avoid the attack, you just blow their brains out. Roll only when the consequences of the action arent obvious, or need to be determined through the arbitration of the dice.