The use of ezplaftorm:reindex is a better way to index content as it is multi-threaded. In a multi siteaccess environment if you want to index a specific siteaccess the only way to do that is to use ezplatform:solr_create_index but this command is not multi-threaded.

If you add the --siteaccess parameter to the ezplatform:reindex command it will not use it because when the multithread commands are built the siteaccess parameter is not used.

the siteaccess parameter should be added to help index a specific siteaccess in multi-siteaccess env.