I do it once a year. I don't drain my house water heater. That is 100gal. With only two of us I am sure I all those gallons of water are not circulated in and out in a short period of time.
One caution about emptying water heater would be if you do drain your water heater after every trip make sure breaker is off so it does not accidentally get turned on without water. If your water heater especially if it has electric capabilities is turned on without water in it, it will ruin heater. Just my opinion.
Yeah but you know the quality of water at your house. "City water" ? Even better.