The beneficial use of computer simulations to track the microstructural evolution of individual species is highlighted in view of macromolecular engineering and design, considering two case studies on catalytic polymerization, and both \"low\" (<100) and \"high\" (>100) chain lengths, that is, i) atom transfer radical copolymerization of n-butyl acrylate and styrene aiming at the synthesis of functional macrospecies of \"identical\' chain length; and ii) chain shuttling polymerization of ethylene and 1-octene toward the production of segmented block copolymers with \"soft\" and \"hard\" segments. Model parameters are validated and/or tuned based on literature data. The modeling strategy supports the future identification of chemical structure-polymer property relationships and is based on the combination of principles from polymer reaction engineering, chemistry, and physics.