Seriously! My dad hooked one up to an old gutter on his shed years ago. He used that water for all his tomato plants all summer long. Never seemed crazy to me, just really practical. Saved him a ton on his water bill too.
Yeah, the part about saving on the water bill is what got me. I always thought they were just for like, hardcore off-grid people. Then my neighbor showed me how full his got from just one decent storm. He waters his whole garden with it for a week. It's basically free water just falling on your house. Kind of a no-brainer once you see it work.