Regarding principal propagation

Hi Experts ,

                    i had a query i.e. what is principal propagation?.

As per my knowledge the principal propagation is used to control access to users.so here my query is we are having this in communication channel and also in sxmb_adm screen .so when we will go communication channel option and when we will go for the sxmb_adm screnn option.please clarify me.

Thanks

Giridhar