Magic is full of cards that belong together. Take the Urzatron lands for example:
Alone, unexciting. Together, powerhouse. In M12, there are a group of three artifacts that have a relationship with each other that bears close examination. They are, of course, the Empire artifacts.
Let's assume for a moment that you're going to play all three of them together in Sealed if you happen to open them, if only because you won't have the opportunity very often. Let's also assume for a moment that they aren't powerful enough to become the cornerstone of a Standard deck. Therefore, let's look at the possibilities in Draft.
The Crown is clearly good in its own right. Yes, three mana is a lot to sink into it every turn, but it's also a small price to pay if it means avoiding getting hit by a Serra Angel, or Sengir Vampire, or anything with a Greatsword equipped. The Throne is also a card that does something on its own, churning out a 1/1 every turn. That's not super-exciting, but it is something that can keep you in the game while you find your cards that are super-exciting.
Then there's the Scepter, and this is where things start to get interesting. It's always an intriguing area of the game when cards don't directly impact the board. You have to spend an amount of mana and a whole, precious card to change nothing about the battlefield, so what it does away from the battlefield has to be proportionally better to justify inclusion in your deck. One damage to a player doesn't sound like a lot. Even if you draw this when your opponent is at something like five live, that's still a ton of time for them to draw an answer. In that situation, even a 1/1 dude might sometimes be better.
What about the upside if you assemble the trinity?
Scepter of Empires still isn't super-exciting, although three damage to the face will end games a lot quicker than one damage a turn.
Throne of Empires becomes close-to unstoppable, generating five 1/1s each turn instead of just one, although you could still die to a random flyer. That's where the Crown steps in, not just tapping the creature, but stealing it instead. That's an unbelievable upgrade.
Alright, so there's no doubt that assembling all three, if you can do it, is incredibly powerful. How often can you expect that to happen?
Now we get into really complicated number-crunching, but we'll try to keep it simple. There are 24 rares in any given draft (all things being equal). That in itself guarantees that there will only be a Throne of Empires in your draft less than 50% of the time. Is it powerful enough on its own that anybody would first pick it? Probably not, so if there's one in the draft you might get it a few picks down the line.
Both the Scepter and the Crown are uncommon, and there are 72 of those (give or take) in each draft. At least one of each should be there. As we've discovered, the Scepter isn't that exciting, although presumably a Bloodthirst black-red player would be more interested than most.
Nonetheless, experience here at Japan Nationals suggests that the Scepter goes late, so if you want it, you can probably get it.
The Crown, however, is another matter. Tapping things is good news, even at a cost. Tapping things with a class of permanent that many decks have difficulty destroying - it's much harder to kill a Crown than a Gideon's Lawkeeper - make the Crown very appealing, and of course being an artifact means that it fits in any deck. If you want the Crown, you're going to have to take it early.
So let's take stock. If you open the Throne, and take it, your priority becomes finding the Crown. If you do that, you should get there, because the Scepter goes late. Of course, you might take a Crown early, get passed a Scepter late, and then open the Throne in pack two or three. Now that would be good times. In reality, though, opening the Throne and trying to put the trinity together?
Good luck. You're going to need it.