A while ago, during the world of laptop batteries, I was told that it was bad to fully discharge lithium batteries. Something about how they were designed made them die quicker (obviously one discharge won't matter here) and they never gain their full charge back again. I've seen this only once, though.
Here's why you discharge to calibrate:
Have you drained a battery dead, then left the device off, came back a few hours later and found it had just a little more life? Everyone should have seen this at least once. What happens is that battery is a multi-cell, each cell does not drain equally and eventually one finally drains completely and the device then turns off. During this period over a hour, the rest of the batteries that hold a charge equalize with that one battery, essentially recharging it. This also creates a crystal buildup and is essentially a bad method of charging.
Now, if you drain the battery to zero, the crystals will build only once and won't occur on this scale again, this is calibration. If you start wall charging too soon or charge before the battery is dead (only before calibration), the battery will build crystals, but it won't build them were they will stop. The battery loses a little bit of life, but is still open to calibration.
Here's something to know: if the battery is left dead too long (days to months depending on the battery) it will permanently die. If accidentally or intentionally left grounded to keep it dead (eg, a manual switch flashlight left on) thinking that would be the best calibration, all the cells will eventually discharge, but the crystal buildup will be so bad that the battery can literally explode (leak their guts) and I've seen this...I've ruined a bose aviation noise canceling headset that way.
Even though the crystals can be built correctly, the battery is eventually going to die because either we can't completely stop the cross charge or the catalyst fails.
Finally, single cell batteries shouldn't have this issue and last longer. Lithium I heard did not build these crystals, which is why I was told you shouldn't calibrate them. I don't know if that is still true. I don't know if these companies researched this or not. Try google.