It relevant for TEST purposes. 100 amps withdrawal of a .060" plate battery is not possible in a 100 amp hour battery. It will have rolled belly up long before.
A true deep cycle battery rated at 100 amp hours, will laugh at the test.
Reserve Capacity is like measuring the ability of a 26-mile marathon runner by how fast he runs the 100-meter dash.
The true, absolute test is the 100 hour test. Far down the column is ampere hours and near the mold at the bottom is reserve capacity.
Unless of course a person desires high performance until the middle of the next camping trip.
(Ridiculous?)