Precise timekeeping plays a key role not only in science but also in many technological sectors, including aerospace, global navigation satellite systems, defense, and telecommunication. Very often, only atomic-based frequency references provide the required stability and accuracy. At the same time, the clocks used in technological applications should satisfy precise specifications in terms of size, weight, and power consumption (SWaP). In this regard, vapor-cell clocks based on alkali-metal atoms pumped by a laser have recently received considerable attention, providing low SWaP joined to interesting frequency stability performances. The spectral characteristics of these lasers directly affect the standard stability performance, both in the short and in the medium-long term.