JAP 5 question

Folks,
My winter project is a JAP 5 that was from a Ransome mower. It is fitted with an Amal 391 carb which has the usual slider throttle control. What is confusing me is that it is also fitted with a govenor which is driven by the engine. Can someone explain please why would both be fitted.
Thank Mick

Presumably so that you can't over-speed the engine using the throttle ?

Thanks for that, I wondered if it could have been linked to the load the engine was under in some way, if you set the engine revs before you started mowing what happened when you hit the long grass.

The 'modern' John Deere mowers I used to work on had air vane governors, I suppose as you say if the engine suddenly has a load on it will bring the revs back up to wherever the throttle is set.