There are advantages to having the filesystem do the snapshots itself. For example, if you have a really big file that you keep deleting and restoring from a snapshot, you'll only pay the cost of the space once with Btrfs, but will pay it every time over with LVM.

On some of my zfs servers, the number of snapshots (mostly periodic, rotated — hour, day, month, updates, data maintenance work) is 10-12 thousand. LVM can't do that.