Regular and irregular variabilities have been observed in several types of stars. Together with variabilities, episodes of enhanced mass-loss are also recently reported in massive OB-type stars. In order to understand these phenomena, I shall discuss about the dynamical instabilities and associated consequences in models of different stars. Interestingly, instabilities of dynamical nature are also found to be present in models of pair-instability supernova progenitors. In the context of ongoing (TESS) and upcoming (e.g. TMT) observational facilities, the role of stellar modeling/stability analysis will also be briefly discussed.