There are a couple of related influences, some discussed much earlier in this thread, but active pitch mechanisms usually result in a heavier rotor assemblies. As much of this weight is added closest to the plane of the blades, it may also require a more robust frame and/or yaw assembly to support it. It may require additional conductors and slip-ring poles.
Adriaan points to the idea that for the system (Category A) to work well depends on the blades having relatively low friction about their axes. I think this is true of both categories, and to achieve this depends not only on the selection of the bearings, and related components, but also on regular maintenance of those components and points of contact (cleaning, lubrication, removal of corrosion). We recently discussed some of the older Dunlite turbines. Although they were a very heavy, robust build (Cat. A type), they often had severe damage over time if they were not maintained.
I do agree that an advantage of the Category B designs is that you also have the added potential of shutting down the turbine. This feature is a significant advantage if there are hurricane force winds on the horizon, or say if there is icing, or a need to climb the tower for inspection or maintenance. In my experience this is one of the best ways to avoid problems; wait out the really rough stuff.
With either category, you will have introduced more complexity. Most of it up on the tower.