Water heaters can be pretty expensive to run compared to most other household appliances, so you want to ensure that they're already performing as efficiently as possible. This is why it's recommended that you drain your water heater at least once a year. If you don't, then sediment can build up inside and cause your heater to exert much more energy to heat water. This is because it has to heat this sediment before it heats the water.
If there is any appliance in your home you want running at peak performance, it's your water heater so remember to give it a good drain about once a year.