Both better performance at range and also for the multitude of users who transfer files between computers on the same LAN or WLAN.
I have a 75/35 package, with usable 80/36 through speed testing. I also have a nice Gigabit LAN and a server with dual gigabit links in part to feed/be feed from my desktop, which also has dual gigabit links.
In the same room as my router, I can get 21MB/sec speeds on my laptop, double what my internet connection can push, but I sit on my back deck, just 30 feet and an exterior wall away, it drops to about 8MB/sec, below the speed of my internet connection. If I had a faster router, I could probably at least max out my internet connection on my deck then.
Or as the case stated, LAN transfers, 21MB/sec transfers a paltry compared to the 114MB/sec I can get plugging the laptop in to on my my LAN drops for big transfers, let alone the 200+MB/sec I get between my desktop and server.
So upgrading my routers to 802.11ac is in my near term plans (I have a 7260 in my laptop now). Even if it just nets me 30-40MB/sec, that would be a nice improvement.