Catalytic active sites consisting in isolated metal single atoms can be found in enzymatic, homogenous and heterogeneous catalysts. In heterogeneous catalysis, single-atom catalysts (SACs) may offer high reactivity and selectivity towards some reactions provided their local coordination environment and electronic properties are correctly tuned. These sites generally possess specific properties compared to metal nanoparticles or clusters. Because of the difficulty, inherent in supported catalysis, of preparing catalysts having a high homogeneity of active sites, these two species have had to coexist in many supported catalysts. If the current trend is often limited to comparing the reactivity of these two types of species, we will see in this mini-review that for few years, work has highlighted a possible synergy between these species to improve catalytic performance. The different types of synergies are discussed, as well as challenges and opportunities for such catalysts in thermal-, electro- and photo-catalysis.