lun ID (optional)

[TDUBB1234]

when I map an igroup to a lun

what is the purpose of the lun id which says optional?

DO I need it?

[JGPSHNTAP]

I don't believe it's optional..

https://library.netapp.com/ecmdocs/ECMP1196995/html/GUID-07173D11-BD59-4BB3-BFC7-61836A9E1A88.html