Honestly, the other commenter hit the nail on the head in that "optimum" doesn't mean "necessary"—but 10 minutes of a commute isn't enough to get your engine fully up to working temperature and you are shortening its lifespan. Maybe it doesn't matter to you, and that's totally fine. If you're changing vehicles every couple of years you're probably not even going to run into needing significant repairs as a result of it, but if you're planning on keeping your vehicles for a longer period of time it's definitely something you should consider.