Upgrading to one of these devices gives a great range of features over standard batteries. One of the main benefits is the ability to increase or decrease the power sent to your atomiser (tank).
Increased power means a stronger hit and more vapour production. This gives you the flexibility to fine tune how you like your vapour delivery and can also preserve battery life if turned down.
Most box mods will also have a battery life remaining gauge to take the guesswork out of when you need to recharge.