Layouts would be more useful if the editor was similar to other IDEs, with bunches of different windows to do different things. Take a 3d modeller for example, which typically has a 3d view(or multiple), at least a window for editing properties of stuff, different windows for animations, such as curve editors and timelines, windows for shaders or materials...Unity is like this as well, with a realtime rendered view separate from the editor view, animator, and other similar stuff.
GMS2 doesn't have all that complexity(not that it is a bad thing). It isn't designed to have things open constantly based on the current task, rather you generally just open the window you need when you need it, or go to it in the workspace if its already open.
I think once they implement more stuff, especially once they include coding on the IDE itself(planned feature), the layouts tool will be more useful. I'm sure someone(maybe myself) would make a particle editor for example, but that window would only be needed when you need it. But you may want to edit sprites and rooms at the same time...you could have a layout for general work, and a layout that moves the workspace and particle system editor windows to good places and sizes so you can easily switch back and forth. That is actually the good point about layouts, you can maximize space on what you need for specific tasks while still making the smaller needed windows available.