Opacity is a measure of the transparency of a gas, and it depends on the gas temperature, density, and elemental composition in a complicated way. Convection is analogous to the turbulent motion in a pot of water as it boils. In addition, convection can only operate if it transports more heat than radiation. The details of the efficiency of convection are not well understood, and they are probably the major source of uncertainty in the study of stellar structure and evolution. A third energy transport mechanism, conduction, is relatively unimportant in stellar interiors.
Convection is likely to be important in determining other properties of the star.
The existence of a hot corona may be associated with active convection in the outer layers, and the depth of the convective layer determines the extent to which material from the deep interior of the star is mixed into the outer layers. Since interior material is likely to have undergone nuclear reactions, which change the elemental abundances, this mixing affects the abundances in the star's atmosphere . These can be observed by studying stellar spectra. They may also be ejected from the star in a stellar wind , and so affect the composition of interstellar gas. The final ingredient in determining the structure of a main sequence star is the source of heat in the interior, nuclear reactions.