Technically no, you did not "harm" your batteries (beyond reasonable use), however you have reduced their lifespan ever so slightly. Basically, if you want the longest lifespan possible then you want to minimize the amount of time the voltage is away from 3.8V/cell, more info here:
Everyone has their own personal preference when it comes to discharge, set your LVC to the max setting your ESC will allow to get the longest lifespan of your packs. Set the LVC to the lowest setting if you want to get the longest possible run time at the expense of nominally decreasing the lifespan of your pack.
The higher the C rating, typically the longer lifespan your packs will last as well.
Experiment with LVC and see how much longer run time you get between 3.7V and 3.4V, you might be surprised that you get less than an extra 30 seconds or so.