In life sciences and materials chemistry, molecular systems are pivotal and studies of their microscopic structures and chemical and physical processes are routinely performed to gain an understanding of the macroscopic function, performance, and properties-these studies can be experimental, theoretical or a combination of the two and, arguably, a strong point of the latter discipline is the possibility to relate molecular and electronic structures to properties and observables. Today, there is a plethora of spectroscopies in use for the characterization of molecular materials and systems and an associated rich variety of theoretical methods to perform simulations of these, none more impactful than those based on time-dependent density functional theory (DFT). The notion of chemically intact subsystems and localized electronic transitions has further led to the development of physically well motivated polarizable embedding techniques that has enabled mixed quantum-mechanical/molecular-mechanical (QM/MM) spectroscopy simulations involving complex molecular systems. However, the size of the QM region can ultimately not be made smaller than the spatially most widespread transition density in the spectral bands of interest.