The main purpose for discharging a pack is to check if the capacity of the pack is still attainable.
I recycle a battery about every six months to make sure I can still put in at least 75% of its rating.
I also recycle if I think the battery is not behaving properly or if it has not been used for a couple of months.
If I don't like the readings I will reform the battery and recycle again or recycle up to 10 times to see if there is improvement.
When I discharge I like to do it to .9 volts per pack.
Obviously, this can only be done with a charger with discharge capabilities and a digital readout such as a GP Triton.
I hope this helps.
Good Luck,
KW_Counter