Labor is increasingly expensive and hard to retain for warehouse work. For piece-picking (the majority of outbound traffic for direct-to-consumer operations like Amazon), the Kiva system reduces the amount of time the warehouse worker spends traveling to find the next pick, and concentrates the time they spend picking (the task that still challenges robotics).
The concept is pretty attractive, but note that Zappos (now owned by Amazon) no longer uses Kiva. And, as Bob Trebilcock says, we’ve seen this story before (closing paragraph).