I usually take the floor leaves and tuck them into a plant or two I actually buy. That way I'm still paying for something and I might get some freebies if I can get the extra leaves to grow but it's not guaranteed. I probably wouldn't do this at a local store tho, just the big box stores.
I don't think it works like that. It's like taking something that's dropped but usable from the shop floor. They might just sweep it to garbage but they probably aren't allowing you to take it anyway.