In an important essay Julian Roberts has drawn attention to the paradox that aggravating and mitigating factors play a crucial role in sentencing, particularly in terms of quantum and around the custody threshold, and yet ‘most guideline systems around the world adopt a laissez-faire approach’ to these factors (Roberts 2008a: 274). Sentencing statutes or guidelines may list the relevant factors, and may even group them, but only rarely do they provide any guidance as to the relative weight of those factors or as to the impact they should have on sentence. The role of aggravating and mitigating factors is therefore left largely without structure, unbridled and untamed, a tendency that undermines the rationale of sentencing guidelines in providing common starting points and shared standards. It may also impair public understanding of sentences handed down by the courts.