I used to think that the padlock design of using many layers of metal stacked to form the main body was a cost-cutting consideration. This was my assumption before I came across the idea that it was really a way to make the lock stronger. It might have been from a TV commercial which showed a bullet penetrating a lock in slow motion. This was many, many years ago, but I have always wondered about that. Although anectodal, my experience finds that really sturdy, heavy duty equipment usually has a nice solid frame or enclosure. I'm not counting things like cars that are designed with "crumple zones", because in such cases weight is a major factor. I'm thinking about manufacture where weight isn't an issue, like padlocks. Does anyone have knowledge of something that would support this claim?
The multi-layered structure protects against impact fracture.
If you hit an object very hard, you can create a crack; stresses will concentrate at that crack, and make it easier for the crack to propagate (think of the little notch in the ketchup packet: that's where you can tear the plastic...)
Now if you have a solid body (of anything), then that crack can continue to grow. But if you laminate, then the crack will hit the end of one lamina, and stop. That means that a laminated object will be much more impact resistant: it's easy to initiate a crack on the outermost surface (for example with a carbide-tipped object), but it's much harder to do so on an inner surface (which your tool cannot reach).
@Floris answer is great, but there is another characteristic of a laminated lock, compared to a solid lock, to consider.
A laminated lock, has as few as 4 pins (6 or 8 on larger locks) holding the laminations together. The pins are basically rivets that run from the top of the lock, through all the laminations to the bottom of the lock, at the 4 corners. On larger locks, there will be additional rivets near the edges toward the middle.
Depending on the characteristics of the impact, these rivets might be the failure point. Breaking even just 1 of the rivets leaves the laminations unsupported and subject to easier penetration. Breaking just 2 rivets (3 on larger locks) will most likely lead to a catastrophic lock failure.