Alternate credentials is the credentials to use for connecting the remote Machine that are stored between sessions of your work with the application. So you can specify the credentials once for Machine, Group or Network and they are automatically applied when it is required.
Although the alternate credentials are stored in strongly encrypted state, it is still possible for an intruder to decrypt the credentials.
Network credentials are used to set the same credentials for all the Machines in the network.
Individual Group credentials are used when several Domains or Workgroups with different administrative accounts are present in the network.
Individual Machine credentials are mainly used to set the alternative credentials for the separate Machines in the network.