The Case for General Cavity Descriptors. The first application of SMART descriptors aided in mechanistic understanding and modeling for dirhodium(II) catalyzed site-selective C-H functionalization of 1-bromo-4pethylbenzene via donor/acceptor carbenes (Figure ). This initial study explicitly quantified that more confined and rigid catalysts allowed for functionalization at the less hindered C2 site. The authors noted direct comparisons showing that traditional Sterimol and Vbur steric descriptors were unable to capture peripheral steric hindrance, the flexibility of catalyst shape, and the resulting variable accessibility of the bound carbene to the approaching substrate C-H bonds. b) The probe shape greatly impacts the shape of the cavity. Flexible probes (AcycH_12) can explore more hindered regions of a cavity than rigid probes (CycH_12). c) Probe substituents also impact the size of the cavity. Small substituents (CycH_12) can parametrize more space than larger substituents (CycF_12). SMART descriptors were subsequently used to model diastereoselectivity in the C-H insertion of donor/donor carbenes for the cyclization of benzodihydrofurans (Figure ). However, due to the steric demands of the intramolecular cyclization transition state, this system required a different molecular probe and a set of proximal and distal SMART descriptors. In this general utility guide, we present a mechanistic analysis of the different SMART methods utilized in these two applications to contextualize the practical considerations analyzed. Parametrizing Dirhodium(II) Cavity Subspace. In the initial SMART application, the full cavity space was parametrized. This proved to be advantageous for an intermolecular C-H insertion as the second substrate enters the catalyst cavity and is directed towards the rhodium carbene (Figure , top). In the intramolecular cyclization, the site for C-H insertion is already within the pocket upon carbene formation, thus the space proximal to the rhodium is likely to be most influential to selectivity (Figure ).