The biggest and most measurable benefit is that it keeps you writing. You can often spark creativity by simply being creative, that is, you write five or seven days per week, and you can fill up that writing time fairly readily. But if you only write three times per month, you may find you have writers' block when you make the infrequent attempt. There is something about the pressure of deadlines or at least the pressure of your own internal expectations. It helps to not have a blank page to stare at all the time.
Never, ever use the word 'by' unless you are referring to an 'edited by' line. Otherwise, just use your name as the author name. Don't believe me? Go to a bookstore or Amazon and look at what's out there.
Last year, it was Terry Pratchett. But this year it was Gene Wilder. And now we have also learned Terry Jones of Monty Python is afflicted. Because this disease shows no mercy. As much as we love these entertainers (and Jones is a medieval studies scholar), Alzheimer's just plain does not care. But we do.