As I understand the basic theory, a camshaft sensor gives the engine management system information essential for the operation of sequential fuel injection.
As you say, a camshaft sensor (or Cylinder Identification Device), gives greater accuracy - the precise position of the engine can be readily determined rather than only knowing if it is in one of 2 possible positions using only a crankshaft sensor.
Stricter emissions control requires much greater accuracy so some systems use 2 sensors and fuel injection timing and duration can be controlled much more finely.
This necessity is demonstrated sometimes when engine running is compromised by relatively small variations in valve timing caused by even slight timing belt/chain malfunctions.
Some engine sensors are subject to heat cycling and are delicate instruments usually made to a cost. They are therefore subject to premature/random failure.
If Space Shuttle technology (usually much more reliable and durable) was applied to cars then maybe only NASA could afford one!
Regards,
Steve
Apologies James, I am not trying to upstage you - I was still hammering away at my response when your reply beat mine to the forum!