In CMDB and ITSM terminology there is nothing called Principle CLass - if you are referring as Parent Class as Principle Class then you do not need any configuration.

This is also relative from Where and which class you areferring to

Like Server is PARENT of LINUX SERVER Class

CMDB CI Hardaware is parent of SERVER CLass

CMDB CI is parent of CMDB CI Hardware class. Its al in hierarchy.

Do we need to identify Principal CI classes as best practice ?---> I am assuming Principle class means Parent Class --> You need to some time identify Parent Class when you are adding custom attributes in CMDB. Why is -so that attributes is needed by which all classes. Like if i need to add a custom attribute called REQ_NO/CR No  against which Server is Provisioned i will add to PARENT SERVER CLass and this attribute will be consumed all below classes like windows/AIX/HPUX/LINUX etc. So here i identified the best possible Parent class for this attribute.

Hope This helps,

Regards

RP