Many places use them now and they are great!
There are a couple of ways they can help:
1) no need to keep a tank of water hot, you only heat what you use
2) save on piping. (Mostly for smaller homes) you only run cold water lines throughout the house and split it where you need hot water. Put multiple small tankless units under each sink and it supplies your hot from the incoming cold line.
3) they heat more efficiently since they use a heat exchanger design, less energy to heat the same volume of water.
If you get a larger single unit, many places will now install them where you use the most hot water so the hot "arrives" faster. Since they are much smaller than a tank design, they can fit nearly anywhere.