Just an example:
Go to an empty screenset you can use, open the browser in the multidock, resize it and have it show folders.
Lock the screenset, switch to another and then back, it will have forgotten the size and that you had folders set to be visible. Now you have to spend time grabbing the mouse putting everything back, resizing selecting to show folders etc.. negating the use of screensets to save time.
There's other things that I can't remember of the top of my head basically things not being exactly the same as when I set it up and locked it,
When I setup a screenset and lock it, I would expect everything, no matter what, to be exactly pixel perfect the same the next time I activated it so I can concentrate on the task at hand, if not what's the point?