Advantages of Controllable Pitch Propeller (CPP) are -
(a) Immediate control of the vessel by the OOW.
(b) The ship can be stopped, without stopping the engine.
(c) Shaft alternators can be used with a constant speed shaft, thereby saving on the cost of auxiliary fuel for generators.
(d) Air start bottles are unlikely to cause a problem during continuous manoeuvres.
(e) Bridge wing and central control positions provide better ship handling.