What does nsurlsessiond transfer? nsurlsessiond makes numerous calls to apple.com over port 80. From other posts I have learned that some of this is iCloud, system updates and similar data. Is there some analysis available about what exact data is transmitted?
nsurlsessiond can be called by so many different things in different cases. You can monitor what's being downloaded using (requires SIP disabled):

sudo fs_usage -w | grep nsurlsessiond