With hanging, done by the British Long Drop method introduced in the 19th century, the executioner can enter the condemned cell as the clock on the prison tower starts chiming for the 8 or 9am hour, and have the prisoner dead on the rope by the time the last note sounds. Strangulation only happens with executions which are not done to that system. It is by far the swiftest and most merciful way of execution.
The drop is calculated according to weight, height and musculature of the condemned prisoner. Correctly applied, it causes an instant dislocation and fracture of the cervical spinal cord, and this means death is virtually instantaneous.
The greatest practicioner of the method, Albert Pierrepoint, performed over 500 judicial hangings perfectly as Number One executioner. All that experience led him to conclude that capital punishment has never prevented one single capital crime.
So if it has no deterrent effect, what's the point?
Lead me not into temptation, I can find my own way there...