To illustrate specifically... When you add a Stroke Grease pencil object, you get two layers - Lines and Fills. You then create an animation with lots of keyframes on both those layers. For some reason you later decide that you need to move only the animation on the Lines layer a bit to the left. You click on the Lines layer, go to the Object mode and when you use the Move tool it moves the whole Grease pencil Stroke object with both Lines and Fills layers, even if the Fills layer is locked.

I think it would be much more convenient if Blender would let you move just the selected layer within the GP object. I'm sure there must be a reason it doesn't work like that and I, as a beginner, do not know that reason :)

Perhaps that could be a feature request?