In a small kitchen
there's nowhere to go but up when you're looking for creative storage options. Counter space is at a premium, so stacking is the way to go.
But this creates a usability problem for those of us who are vertically challenged - I'm five foot nothing, and it's a constant struggle to haul things down from high cupboards. Even for those taller than myself, this can be a problem when shelves are stacked up to the ceiling.