Some researchers devised a predictive model which examined how cycling your battery at lower states of charge extends its life:
Basically, these things shorten the useful life of a battery:
Spending lots of time at high states of charge
Being discharged from high SOC to low SOC
Discharging the cell at rapid rates
These things extend the life of a battery:
Spending lots of time at modest SOC
Being discharged from modest to low SOCs
Discharging the cell at modest rates.
Things like discharging between 60% SOC and 0% SOC was better than discharging between 100% and 40% SOC.