In superuser app what does force user do and what are there meanings
Net_BT, Inet and so forth, are special users called AIDs (Android IDs). Those users are each in charge of a particular component of your device. The Force user option, when coupled with one of the abovementioned AIDs, lets an app act as one of those, granting it full power over the AID's specific domain.

If you think about the AIDs as kings, and root as a god, then there's usually no need to impersonate one of the AIDs, for root has power above each of their domains.