Good input from everyone, but I am itching to correct a few misconceptions.Lithium-based batteries come already caliberated by the manufacturer hence, you do not need to worry about keeping the battery between 20% and 80% or any other figures out there. 100% on your phone, isn't actually 100% on the battery and 0% isn't actually zero.
Secondly, using your phone while charging is discouraged to avoid injury just in case the battery explodes (which only happens if it is defective or you're using a bad charger). Otherwise, if you're using your phone as you charge it, it will do something referred to as "trickle charge" which is simply the battery taking in small amounts of power.
Thirdly, you can charge your battery for 12 hours straight if you want to, but with the technology used nowadays, once your battery gets to 100% it stops taking in power and the power is fed directly to the phone.