Is it best to constantly be charging a device when not using it?

Should a device (Li-ion battery) be charged all night and used all day?

Is it good to fully drain a battery before recharging?

Is it better for a battery to remain as full as possible as often as possible?

I'm asking because I have a PowerBag Backpacl with a 6000 mah battery built-in so I can charge my phone and tablet throughout the day. Assuming I leave the tablet plugged into the backpack, and charge the backpack battery and tablet all night, then leave for the day, if I'm say pulling out my tablet and using it for a half hour every couple of hours, should I be recharging it in between or just leave it and charge it again overnight, or keep using it for a few days until I totally use up the charge.

Thanks guys.