Using this option allows for more baserunning decisions because it does not follow the board game rules for baserunning. For instance, using this option you will often be asked if you wish to send a runner from first to third on a Single* or a Single** reading. In the board game Single* means a single with runners advancing one base and Single** means a single with runners advancing two bases (it is automatic in both cases, no option exists).
This option also allows certain base hits to be stretched. For instance, some singles will have an option to be stretched into a double, some doubles to triples and some triples to inside the park homeruns!
See the Maximum Rules page for more information.