3/15. Improved Performance
Doing planks every day will provide your abdominal muscles the adequate strengthening necessary for performance. Once these muscle groups are strengthened, you can perform daily tasks optimally, lift heavier weights and objects, and perform other sport activities with agility.
4/15. Back Strength
Unlike some other bodyweight exercises (crunches, etc.) that hurt your back, doing planks every day will strengthen it. Plank requires no movement and the position recruits your back muscles particularly your upper back while straightening your spine. More so, because your glutes are involved, your lower back is also protected and getting strengthened as well.