Not necessary for every possibility. However, some features, especially one engaged potentially several hundred times a day and is new, is reasonable to have choice. Apple provides it.
Most people outside of those on tech forums may not know that particular option exists because all previous home button's were simply buttons, and could go for months or years not knowing there's a choice.
ESPECIALLY because after nine years, this is the first taptic Home button, and that it can be customized. Ordinary people (those who are not into tech) should be alerted to that with being able to make a choice during setup.
Nice that Apple took the time letting people know that something that is brand new and engaged so often during the day can be personalized. Takes a couple seconds. Life goes on.