What’s Carhart’s effect (not notch)? Is is beneficial or harmful for patient? Please explain 
Association of the dip in BC with CHL is known as Carharts effect .
It is just a representation of stapes fixation.
If you are asking it being beneficial or harmful in the sense whether it is correctable or not — it is correctable with surgical mobilisation of stapes footplate as compared to other depressions in BC which represent SNHL and are not correctable