Muscle mass, especially if it includes a lot of actually useful muscles and not just the ones that present best, is very good to have especially once your muscl

Muscle mass, especially if it includes a lot of actually useful muscles and not just the ones that present best, is very good to have especially once your muscle mass starts declining inevitably later in life. Also, along with the muscle usually follow stronger tendons, joints and bones. All those develop through loading. Good core muscles will protect against a lot of injuries and will make you much less fragile. Both physically and chemically (for example, by being able to buffer blood sugar). The stronger the muscle, tendons, joints and bones you start with, the longer you will enjoy not being fragile. But I do agree you can reach the point of diminishing returns very quickly and focusing on muscle doesn't make sense assuming you spend effort on other healthy activities like low intensity aerobic exercise, high intensity aerobic exercise, flexibility, etc. I do weight lifting and calisthenics session, once a week, to strengthen my muscles, tendons and joints to help with my running and from what I researched it should be enough to greatly reduce my chance of running injuries.