Do you recommend excluding anything from a scan?

ANSWER  No.

Many network administrators attempt to pick and choose which systems they should include in an assessment; however, we strongly recommend each organization include every system within their network

Many devices come with configuration settings that may put your network at risk a lot more than you could imagine. For example, many administrators don't believe that printers are necessary to be included as part of a penetration test. However, there have been many cases of penetration testers getting domain administrator access by just simply redirecting LDAP on a printer to their system because the printer was not configured to use any strong, complex authentication credentials.