There are situations where not only ringtones but even vibration noises are unwanted, so a quick switch for this would come in handy.
There is already the “mute” button in the top menu for sounds so I would like to suggest another quick button for switching the vibration on and off. This could also be realized in form of a three-option cycling of the mute button: Ringtones on >> Ringtones off >> Ringtones and Vibration off. Or an additional popup menu option at long-press of the mute-button.