[AndreasPassat]

It basically boils down to the cam sprocket not being loose on the bank 1 camshaft. With the cam sprocket being loose (by loose I mean just enough to turn on the tapered portion of the camshaft). When the camshafts have their static timing set to the timing marks on the cam caps and the static timing on the belt set by the marks on the crankshaft pulley relative to the marks on the plastic cover, then the diamond shaped keys will be exactly horizontal. Basically it allows you a finite adjustment that retarding or advancing the belt by one tooth can't achieve.

 

[AndreasPassat]

I'm gonna chime in here on this timing gear thing.

First off, I assume instead of gear we are talking about the cam pulley on the exhaust camshaft.

Rotating the engine before those cam pulleys are fully torqued can cause the cam pulley to slip radially around the camshaft which in turn will cause the static timing to be off. If off far enough, the pistons will hit the valves.
I'm with PZ on this one, not just because he mentioned it, but because it is a bad practice on the B5 V6 motor.