When you reduce the flow of hot water you also reduce your use of energy. In our house we have two levels of water flow reduction. First our house is connected to the municipal water through a pressure limiting valve. It was probably originally put in because this areas may have too much water pressure, which can cause household appliances to malfunction. Safe pressure is usually less than 10 bar (145 PSI). We have turned this down to 2 bar (29 PSI).
In addition to this we have added faucet aerators on all outlets, except for the one at the bath tub. The faucet aerator introduces air into the flow of water coming out of the faucet. That makes it seem like more water is coming out, but it's actually using less water. I have installed two different types ( http://www.clasohlson.no/vannmengdebegrenser 30-9848 and 30-9849). The claim was that they will reduce the water flow with 40%. I have measured before and after the installation, and the reduction was almost exactly 40%. So whenever someone is washing their hands, less warm water will flow, and there will be a reduction in energy needed for heating water. Our kids often drink cold water straight from the faucet, which is not quite as comfortable to do with all the air introduced, so this is a slight drawback. They complained the first day, but did then get used to it.
Here is an article from EPA about water flow reduction: