Neutrinos have been related to some of the most puzzling phenomena in particle physics, being flavor oscillations one of their most interesting aspects. Here I will focus on the importance of neutrino oscillations in several scenarios. Firstly, I will discuss how they affect the determination of the effective number of neutrinos, a parameter of the standard cosmological model. Finally, I will also mention the role of these elusive particles in determining the lowest possible reheating temperature of the universe.