In the beginning it's important. Physical attraction, mental attraction and emotional attraction. As time goes by its importance diminishes, over many years. After having sex with each other several thousand times, it no longer has the urgency and demand it did when the relationship was new. It's still just as pleasurable, and chocked full of meaning.
At Bill and I's ages this is fine, because, for example, a severe back-ache that's lasts for a few weeks because of an injury puts a damper on the sex drive. So does a flare-up of arthritis and a host of other problems. (Think about how sexually charged you feel with an abcessed tooth, for a comparison).