Piggy-back shocks: Pros/Cons?

[simplechamp]

What are some of the pros and cons of shocks that have piggy-back reservoirs? I know the tech comes from full-size off-road vehicles, but do the effects of having a reservoir remain even when scaled down to RC vehicle sizes?

I really like how they look, but I'm not going to drop the cash on a set if they are purely aesthetic without any performance increase.