VEHICLE_FLAG_CAMERA_DECOUPLED is incredibly useful for use in vehicles, and allows for scripters to create a stabilized platform on otherwise uneven or rough terrain. This was attempted to be brought up in https://feedback.secondlife.com/scripting-bugs/p/llsetvehicleflags-vehicle-flag-camera-decoupled-does-not-work

In said thread, it was elaborated on by the lindens that VEHICLE_FLAG_CAMERA_DECOUPLED requires VEHICLE_FLAG_MOUSELOOK_STEER or VEHICLE_FLAG_MOUSELOOK_BANK

This limits the usability of a desirable function and requires scripters to create work arounds if they are creating some form of track or wheel driven vehicle they want to stabilize.

Additionally, without the ability to decouple non mouselook driven vehicles, they are very nauseating and difficult to control, creating an opportunity for physics grief to negatively impact user experiences. A lack of decoupling for non mouselook steered vehicles was previously worked around for LLCS vehicles, prior to the implementation of llSetLinkSitFlags(link,SIT_FLAG_NO_DAMAGE), by setting the volume detect "sit prim" to be a mouselook steered vehicle that didn't actually make use of any vehicle movement.

In short : The current functionality of VEHICLE_FLAG_CAMERA_DECOUPLED is limited to mouselook steered vehicles, limiting usefulness, the desired functionality of this flag as shown by the existing feedback threads regarding this very topic is use with non mouselook steered vehicles as well. Additionally, camera decoupled vehicles are more user friendly and less prone to being griefed via applying rotations via physical prims as well.

feedback threads in question: