This read-only Integer32 (0 to 2147483647) reports the current number of session groups configured within a session set. An admin cares because this count should align with the fault-tolerance mode of the set (up to two groups if fault tolerant, only one if not), so seeing an unexpected count flags a configuration mismatch. For example, an operator verifying a fault-tolerant set is properly redundant would confirm this object reads 2, indicating both a primary and backup group are present.