The theoretical basis is very simple – based on observations of many groups, experience shows that small groups (8-15 people) formed from unknown individuals follow recognizable, characteristic behavioral patterns, regardless of the individuals. The behavior of individuals is not predictable, but that of a group composed of individuals is, precisely because the group always changes the behavior of individuals in the same, predictable way.
The behavioral pattern of a group is generally recognizable, and based on this, many things can be predicted and foreseen. In practice, organizational groups also operate as groups formed from largely unknown individuals, so the findings of group dynamics are very likely applicable to them.
Knowledge of group dynamics helps us to recognize where a given group stands and when, and what interventions can help in moving forward. Generally, if managerial interventions are in line with the group dynamic situation (rather than opposing it), the group can develop faster with less effort. There is therefore an "natural" order to group development; if development occurs in harmony with this, it leads to results much faster and with less effort.
We do not know the reason for the observable regularities. Small groups may have been a key unit in human history for a very long time. If a small group was able to become effective quickly, this could have been an important selective factor, an evolutionary advantage, if individuals possess "built-in" patterns or programs that accelerate their cooperation and improve their collective problem-solving ability.