You need to understand what merge load does. It can be a useful feature, but only in very specific situations.
When you load a scene, the first thing Vam does is remove all currently loaded scene elements. Then it loads the new scene.
When you merge load, the "unload all currently loaded scene objects" step gets skipped. All the original scene elements stay in place, but then get modified if there are differences between the old and new scene elements of the same name.
In practice, using merge load only really works successfully if the scenes have been designed for it. If the two scenes contain exactly the same objects with the same names, merge load will update all those objects. But if you have a dildo (or something) in the first scene that isn't used in the second scene, it will still be there. And if the person names are different between scenes, new people get added rather than existing people getting new appearances.