As an amateur engine builder I'd like to step in here if I may. I've spec'd out cams before and even created the custom grind bump stick in my twin turbocharged 440.
Let me break a motor down into simple parts to allow non-gearheads to understand things a little better.

The throttle body and intake manifold are like the mouth. They let the air get into the motor. A bigger mouth can draw air easier than a smaller mouth. Opening the mouth too wide does nothing for you. You can't run down the street any faster with your mouth wide open, right?

The cylinder heads are like the lungs. They separate that mouth full of air into useable portions and direct it as efficiently as possible to the place where the work is done. You can run faster with a set of healthy lungs than you can with lungs full of tuberculosis.

The pistons are like the muscles. They push the bottom end around and make it go. If your muscles fail, you fall down and go boom. If your pistons fail, motor go boom. Wallet go boom. You fall down go boom. Wife go boom up side your head. Boom again. Boom. Boom. Boom.

The crank is like the legs. It turns and makes things go. The crank spins the flywheel and/or torque converter and connects the power to the rest of the drivetrain.

The cam (or cams in our case) is like the brain. Without it, nothing else matters. It tells the heads (lungs) when to take that air in and when to let it out. It also tells the heads how much air to let in and out. That's where the witchcraft comes in.
A successful cam relies on several major measurements and they all must work together. Those lumpy lobes sticking out all over the cam are incredibly intricate.
Lift: this determines how far the valve opens and therefore how much air gets into and out of the cylinders.
Duration: this determines how long the valve is open.
Overlap: this tells you how long both the intake and exhaust valves are open at the same time.
Lobe separation angle: this tells you how long both valves are closed so the ignition can take place and the piston can make power.
Cam centerline: this tells you how to physically align the cam with the crankshaft for optimum performance. It sets the timing of the whole cam.

Designers have to take all this stuff and mash it into something that's going to work with the rest of the combination. Stuffing a HUGE cam into an everyday motor isn't going to make anybody happy. It won't match the heads, intake, compression, or rest of the car. That's one of the most common mistakes made by hot rodders.
The engineers have to tell the cam when to open the intake valve, how high it should be held open, and when to close it. That's got to be matched with how much air the throttle/intake/head combo can flow and timed perfectly to the piston movement.
Next, they've got to tell it how long to keep both valves closed so the spark can burn the fuel and let the exploding gasses shove the piston down the hole.
Then, the designers have to figure the optimum time to open the exhaust valve as well as how high it needs to be and when to close it. This is critical to get all the burned nasty stuff out so the engine can have a fresh breath that isn't contaminated with exhaust.
Generally, before the exhaust valve is fully closed, the intake starts to open again. This is known as overlap. The air in the cylinder is already rushing out the exhaust valve and isn't likely to change direction. Opening the intake a wee bit early gives it a head start so it can be open further when the piston begins to move down. That means the vacuum created by the moving piston has a better chance at drawing more air.

At 6,000 rpm, each valve is opening 50 times per second. That means the valve is thrown open nearly 1/2 inch and slammed closed in less than .02 of a second. That's fast. Ugly fast. Don't get your finger caught in there. Every valve cycles a dozen times in the blink of an eye. Literally.

A naturally aspirated engine, supercharged engine, and turbocharged engine will all have different preferences.
The N/A motor needs a balanced cam because it relies on atmospheric pressure to push air into the motor.
A crankshaft driven supercharger will respond better to a similar cam but doesn't need to worry as much about the overlap. It's cramming air in faster than the engine can take it. Hanging the exhaust valve open while the intake is opening will let the blower shove the bad air out so you get an even cleaner burn.
An exhaust driven turbocharger is the exact opposite. The exhaust being pushed out of the engine drives the turbo. It's kinda like a whiffle ball stuffed in the exhaust pipe. It slows down the exhaust flow and creates pressure in the exhaust manifold. That same pressure is the glorious force that spins the turbo and shoves air into the engine faster than it can breathe on it's own. That's the same kind of pressure the supercharger makes. That exhaust system pressure is what separates a turbo from a blower. In all but the most extreme engines, the exhaust pressure will be higher than the intake "boost" pressure. If the cam holds both valves open at the same time, that nasty exhaust pressure will prevent the exhaust from getting out and pollutes the clean intake air. There's a fine balance between closing the exhaust and opening the intake. You still want that head start on the good stuff but don't want the bad stuff hanging around any longer than possible.

Quite often, a stock style cam will favor a turbo over a blower. The same ideas that reduce emissions (low overlap) work in the turbo's favor. The blower's extra little benefit of shoving the bad air out is minimized. The low overlap also makes the engine more efficient at low rpm. They idle smooth and quietly. When the overlap starts to get big, the engine is not happy running slowly. The dirty air isn't moving fast enough to get out and contaminates the intake charge. The result is a lumpy bumpy idle that makes a hot rod sound all mean and pissed off.


What this all comes down to is that you can open a valve the same distance with two different cams but when and how long it happens will make all the difference in the world. You can really go off the deep end and even look at how quickly you open/close the valve. Think back to high school algebra when you had to calculate the area under the curve. More area means more air flow.
You can compare it to a dyno chart too. Peak power is useless if there's not a big fat curve on each side, right?

Voodoo, witchcraft, black magic, Physics and the Land of Geekdom, whatever you want to call it, there's a lot more to cams than the numbers you see on paper.

Clear as mud?