This is natural. These sub-groups are beneficial to their members, who form stronger friendships with people with whom they share an intense common interest, and beneficial to the larger group, which gains in vitality and love because of the strengthened friendships which have developed. Unless the sub-group becomes a clique. Cliques are inward-turned groups. They become more interested in intensifying the interactions between their own members, to the detriment of the larger group.
Cliques sap the vitality of the larger group.
In any large group, leaders will emerge. This is natural. And beneficial to the group. These leaders who emerge are usually the members who are most interested in sustaining and enhancing the vitality of the group. They are the ones with the time, energy and desire to organize, energize, harmonize, and strengthen the group.