Geometric networks are objects within the geodatabase. ArcGIS automatically maintains geometric networks when you edit their feature classes.
To work with a geometric network in ArcMap, you must load a minimum of one feature class that participates in the network. If you want to work with only the feature classes that participate in the network—for example, if you're performing analysis on the network—then you can load only those feature classes by loading the network object.
If you want to load all the feature classes in the feature dataset that contain the network—for example, if you want to produce a printed map of the network—you can open the network by loading the feature dataset that contains the network.