It may be that by requiring a larger battery, the recharge load will be reduced.
Guessing here.
But for example, Taxi driver parks by hopsital and turns off engine, but leaves two-way radio on.
After 5 minutes the battery capacity is reduced by 10 amp-hours.
This is a bigger fraction of a 65 amp-hour battery than a 100 amp hour battery. So maybe with a 100 amp hour battery, it won't demand as much amps for recharging when the engine is restarted. Better for the wiring and better for the battery.