CCleaner Network analyses all your hosts and gives them a score indicating how Clean or Defragged they are. 100% indicates perfect health, whereas 0% shows that the host really needs attention.
There are Health scores for each Network as well as for each Group.
The Health scores are an average of all the Clean and Defrag scores for the hosts in the current Network or Group. For example, if you had a CCleaner score of 60% and a Defraggler score of 50%, your Health would be 55%. This Health is then averaged over all the other hosts in the group to give you the Group Health.