ScriptId allows you filter on the ID of the Script associated with a Script Run or Script Assignment.
This field and the Script field can both be used for searching by ScriptId - but key differences are that:
Matching by single Id:
ScriptId = 07649a3b-f086-4d0d-94b8-a14d00850fe9
Matching by multiple Id's:
ScriptId IN [07649a3b-f086-4d0d-94b8-a14d00850fe9, 91f8769a-1f02-4201-9c85-a14d008e9a43]