Variable valve timing can describe a lot of different ways to change the relative position of the camshaft to the crankshaft. Typically a phaser is used to advance or retard the cam relative to the crankshaft.
The phasing can be used for a number of different functions. The primary benefit of interest to us is to increase the width of the powerband, but it can also be used to improve emissions and fuel economy.
Seems like if it is off just a smidgen that the engine would be eating valves at higher rpm's. But such is modern technology. What happened to shade tree mechanican? Went out the window with the first black box.