I've seen a few posts on the internet that say that water heaters should be flushed every year and "I bet you never knew you should be doing this!" After searching around most of the articles that explain why this is the case also include that "by the way, our company can provide this service for you" - so I'm a little skeptical of the actual necessity. I found one article that stated that most water from municipal supplies is good enough that it won't cause sediment build-up and doesn't require flushing. I've also seen an article describing how flushing old tanks could actually cause leaks by removing excess build-up that had been keeping them plugged.
So who actually needs to be flushing their hot water heaters regularly? For my own situation we live in a major US city and have a 3yo gas-powered tank heater. I'd expect ours is in good shape currently but want to make sure we're maintaining it properly.