Tom's reply below illustrates just one issue with layouts as they were implemented in Pro/NOTEBOOK. I am specifically not talking about any modifications or enhancements implemented in Creo Layout.
While you've accurately described the PTC sales literature proclaiming the obvious benefits of a layout, in practice, it's a tremendous pain in the neck to manage. Declaring parameters back and forth is just one issue. If you ever wish to "back out" of the layout once your design has matured, you cannot. You're forever stuck having to manipulate your assembly with a complex series of relationships established by the layout. Although the promise of the layout is to gather engineering information in one location, document it, pictorially illustrate critical design parameters, and then share them to all relevant components, this is far tougher than it needs to be.
Creating illustrations alone was a huge hassle in Notebook. Go ahead and open up a new Notebook in Creo 2.0 then try to draw a BOX (literally a rectangle) and place two dimensions on it. First of all, you cannot sketch a rectangle using any normal means... you're drawing with sticks connected together... one line at a time. You're looking at a minimum of 12 clicks (I counted 15) and you'll have to mess with it for the sketch to look remotely decent. Now imagine trying to sketch a complex interaction between numerous components that are not as simple as a rectangle. Saying the layout illustration is akin to the sketch on a 'beer napkin' is unfairly maligning beer napkin sketches.
You cannot even steal a decent view of geometry from another Creo model. Sure, you can use an overlay, but you cannot dimension to it... making it useless. Unless you wish to export a DXF from Creo so you can re-import it to your notebook, you're out of luck. Why? Seems pretty foolish in 2014 to need to use such draconian tactics to force such a vaunted piece of software to live up to the sales pitch.
Then there's "automatic assembly of hardware". This was a big selling point! Imagine being able to automatically populate an assembly with the appropriate hardware from the layout. Wow... impressive... except when you have to edit a ridiculous table that's 5000 feet long to make it work. Oh, and then you have to go back and name every single reference on each component and each piece of hardware, declare it, etc. It's horrible.
I would sooner add all of the design intelligence to a PROGRAM embedded in the models than I would use Notebook. At least I can use a script to strip off the program when I'm done using it for design iteration and investigating 'what if' scenarios. Notebook, by comparison, is cumbersome, overly complicated, requires far too much setup, cannot be removed, has child-like tools that remind me of the "state of the art" in CAD (back in 1996), and so few people understand it, you're stuck perenially retraining every new hire to comprehend the mess you've created in the name of 'saving time'. PTC put out a masterful sales pitch for this product. But it worked for only a precious few customers and ultimately failed to deliver. Top down design and skeleton techniques have far eclipsed this tool. Perhaps Creo Layout is worth taking a look at but I have to stand by my original statement on Notebook.
Yuck.
