Tankless Water Heaters

Today I learned that tankless water heaters for homes are real.

The reason this surprises me is that I've never seen one. I watched a video on the web where the guy claimed these things are new technology, however a person from Spain left a comment saying he has never seen a water heater with a tank.

Great.

So why the hell am I keeping a giant tank of water hot 24/7 when I use hot water once a day for about 10-15 minutes? Why has Spain had this supposed "cutting edge" technology for years while we here in the US go to work and earn money to have it disappear into the ether above our idle water heater tanks?

Lastly, why couldn't I have heard about this 3 months earlier when the Federal tax break of $300 would still apply to this type of appliance purchase bringing the hardware cost down to about $400 for a beautiful Bosch tankless gas heater.