It is at the outskirts of many towns and villages where it’s not been clear what the speed limit should be. With minimal development there can be little perceived reason to traffic to reduce speed. The presence of a Vehicle Activated Speed Sign gives the clue that speed limits are in disrespect, the sign itself often being lit continually with a stream of vehicles. Meanwhile pedestrians can be misled into believing traffic speeds are lower than the posted speed limit and so behave inappropriately.
In the photo above the vehicle has slowed due to pedestrians crossing the road for a public footpath. It’s this driving to conditions and use by road users of all types that the DfT Guidance aims to build.

The first phase to review a speed limit would measure mean traffic speeds.  An assessment of local development and use of the road determines the value of limit (no lower than those mean speeds). The position of the speed limit signs reinforces the boundary of urban features. 
Using the Guidance to determine speed limits should benefit all road users.