Ohh wow. I have just gotten some weird glitches. The goal was to exclude some meshes from postprocesses like here Sharing depth buffer between two cameras - #8 by Evgeni_Popov. But when I parent the camera it glitches out. So parenting is off the table.
So, just do what @labris said 
An alternative (havent tried yet) might be using one of these: camera.onAfterCheckInputsObservable or camera.onProjectionMatrixChangedObservable. This way you would only update the camera if it actually changed. But it is more code (listener tacking/cleanup).