degreeing a cam / Intake Centerline

It's for all of the above and then some. Not only to make sure the camshaft is ground correctly, but to assure it is in the engine where it is supposed to be in relation to everything else. Also, there's absolutely no gaurantee that the timing chain and gear set is machined exactly right. No gaurantee the crankshaft key is in exactly the right place. Beyond the mere physicalities of it, a lot of engine builders like to experiment around with putting the camshaft in the engine in different places in relation to crankshaft rotation. So, to do that you need to know where the camshaft is in the engine and the only way to do that is with a degree wheel.