If you wait until it is totally discharged then you are guaranteed to run out of battery just when you need it.
You may be thinking of the the older Ni-cad type rechargeable battery.
It was (and is) a good idea to discharge them completely once in a while. This stopped them from gaining a memory effect, which would reduce the amount of charge they would accept.
But with the later Li-ion type battery this problem does not occur.
So you are safe to charge your phone whenever it suits you .. I just charge mines overnight. Older phones seemed to hold there charge for days, but a lot of smart phones only seem to last a day.