Basically, I think it’d be neat if, when you draw a new shape with the Pen tool, the tool could snap to a nearby shape’s vector nodes (or edges!), allowing the user to draw shapes that neatly align with each other.
There’s already this kind of snapping behavior with existing geometry within a network, so why not give us the ability to use it with outside objects?
I agree, it would be a bit hard to control which objects you want to snap to. For that reason Illustrator has isolation mode, so it quickly makes things complicated.