The Minimum Length setting gives the user control, when placing couplings, over the minimum length of conduit that will be left connected between the connector of the conduit bend and the connecter of the coupling once placed. So how much of a tangential piece of conduit is left on the end of the conduit bend before the coupling.
The Maximum Length setting gives the user control, when placing couplings, over the maximum length of conduit and conduit fittings between two couplings or between couplings and conduit ends. You can think of this like the stock length setting which is the length we are trying to hit when placing couplings.
The Round Conduit Length setting give the split tools a goal for rounding conduit run lengths between couplings. This establishes more of an affinity for those nice rounded lengths when you cannot get a full Maximum Length out of a section of conduit but will be bound to the geometry, nonetheless.
If you draw a piece of conduit that is 11′ 8-3/64″ long with a Maximum Length of 10′, no amount of rounding settings are going to change the fact that the measured length from end to end will stay the same, though you will have at least one 10′ piece if the geometry allows it with bends considered.