Is it just for looks?
In desktop keyboards yes. However, people seem to like the snappy response which is of course bought at the price of bottoming out way too early. I'd guess the rubber domes are slower when they are pressed beyond their tactile phase. So if you avoid that they're snappy.
Or even cheaper to produce?
Not than std. rubber domes but cheaper than mechanical.
Lower hight in laptops?
That's where it started. These are still rubber dome with membrane boards but the mechanism that leads the key folds together under the keycap allowing for a flatter design.
New findings on ergonomics?
No. Ergonomics are worse because the keycaps are not angled. So you have to reach farther for the upper row, for example. However, you can push the keycaps at the edge and they will go down perfectly because of the scissors (the opposite edge is pulled down). If this whole scenario is desirable though, I don't know.
