Cynically, it makes layoffs a lot more opaque. When everyone gets to express their individuality by sitting in an identical, constantly-shifting workspace; you can't "walk by" someone's desk and notice it's cleaned out and their gone.
I don't think that's the main reason (the main reason is trying to cheap out on office rent and ape corporate fads), but it's probably a happy added perk for those who are pushing these things.