Whenever administrator logs on to server, he can see all printers created from all the sessions running from server.
Sometime there are application(published through Xenapp) users who gets printers from othere users in thir sessions. In order to stop printers from other sessions mapping into your administrative session, one registry tweak needs to be done.
This will disable connections of Session Printers during logon and reconnection.
This registry can have different values depending upon various requirements. You can find other values and their impact here.
Earlier in older versions, a registry flag called DefaultPrnFlags was used to modify advanced printing options.