Taking the batteries down to less than about 20% SoC will have a very slight effect on the longevity of the bank, but IMO this is negligible. Keeping them at high SoC (> 80 %) for prolonged times is much worse.
In practice, lowest acceptable SoC on LiFePO4 is more a question of preference and of course safety considerations rather than a technical rule
that should be obeyed.
You will likely replace the bank due to technology improvements rather than bank „health“ status if you just use it and follow the simple rules:
Don’t overcharge, stop charging
when full, don’t keep it at high SoC for prolonged time, don’t discharge to 0 % (< 2.8 V Vpc), store and isolate bank at about 50 % SoC for prolonged absence.