I get it.
So if you go through the effort of rooting through all the personality Groups used by the races and listing them out, you can decide the following for your personality group number:
A) You can pick one that is heavily used by other races, which will guarantee that your race will not be seen much in random games.
B) You can pick one that is used infrequently by other races, which will mean more play time for your race.
C) You can pick one that is not used, which will mean that your race will bee seen in most games that use random race selection.
And finally, you can ensure your race does not play against other races by making sure your personality group is the same as that other race.