StringBuilder is more efficient than string concatenation, especially when the operator is repeated over and over as in loops.

Noncompliant Code Example

Module Module1
    Sub Main()
        Dim foo = ""
        foo &= "Result: "       ' Compliant - outside of loop

        For i = 1 To 9
            foo &= i            ' Noncompliant
        Next
    End Sub
End Module

Compliant Solution

Module Module1
    Sub Main()
        Dim foo = New System.Text.StringBuilder
        foo.Append("Result: ")  ' Compliant

        For i = 1 To 9
            foo.Append(i)       ' Compliant
        Next
    End Sub
End Module