I never undrstood who would want to buy these power modules like Enpirion before. They are very expensive compared with building your own 4A converter, and all they offer really is integrated magnetics (also the reason why the package is so thick).
It seemed to me like this was a good idea for prototyping and gettig something out the door quickly. But for serious products built down to a price, doesnt make much sense at all.
Actually, they are quite useful for a lot of reasons:
1. Just-add-water philosophy. All you need is a few extra components which you can source from pretty much anyone with very little fuss. Compare it to rolling your own: Source the inductor, source the caps, the main IC, diodes, FETs... Here all of the critical components are given to you.
2. Optimized spatially - you'll have to try very hard to outperform things like these modules in terms of power to volume ratios. For a similar construction you'd need more board space and you might still not get the same specs. See the
http://www.ti.com/ww/en/simple_switcher/qfn-package-modules.html#nano nano series for an extreme of this.
3. Optimized performace wise - to get a good DC DC converter, all you need to do these days is slap together a few components that have close-enough specs. To get a really good DC DC converter you have to pick your components for quite some time, test them, poke and prod them, test the whole setup... In these modules someone did it for you. As they did the EMC testing. Also the mechanical design. Essentially, this:
http://www.ti.com/lit/ds/symlink/lmz31530.pdf gives you 30 Amps from a package the size of a 30Amp inductor, without any hassle.
Yes, at the end of the day you are just saving time. They offer nothing you could not do on your own, eventually, with the right tech (which might get costly). But it
can (depending on the situation)save you time, board space, efficiency.
edit: This one's nice as well:
http://www.intersil.com/content/dam/Intersil/documents/isl8/isl8273m.pdf