Question

Could there be any specific reason why one can choose UBound over Length?

Here is the code and 1-dimension is passed as second parameter.

    For iIndex = 0 To UBound(myList)
        If Left(Request.ServerVariables("REMOTE_ADDR"), Len(myList(iIndex))) = saIPList(iIndex) Then
            bAuth = True
            Exit For
        End If
    Next

Any performance gain against Length

Answer 1

They do different things! UBound gives you the last index in the array, while Length gives you the length. Those are not the same, because usually UBound will be Length - 1.