If you continuous charging at 100%, the battery will drain over certain time, then the phone will charge up again. So, this will became a loop, drain, charge, drain, charge...And this will reduce the battery life. The battery life is depends on charge cycle.
Yes, the most suggested is to charge it when it is near 35% until 95%. The less time you plug the charger in the device, the longer the life of the battery can last
