What is the purpose of SkyCam?
Image Credit: NASA/JPL-Caltech/CAB
Meteorology is a significant component of this mission, it's just talked about much less than the geology. So we have a fixed camera on the rover that points up.
SkyCam is but one of the sensors used to study the weather and climate, but its specific tasks include tracking changes in cloudiness, dustiness, and the vertical structure of the atmosphere.
Some seasons are far cloudier than others (summertime and aphelion come to mind - the latter occurs when Mars is further from the Sun), so that's easy to track with this instrument. The amount of dust in the atmosphere, and the layered structure (both of which change on a daily basis, as I understand it), are tracked through observations of the sky's colour and brightness.
Pretty fascinating stuff, actually. From my perspective the Martian atmosphere is more... let's say, revealing and honest, than the heavy, sodden blanket around Earth, or the colossal monstrosity around Venus. It's responsive to temperature changes and solar influence in ways that the terrestrial atmosphere would mostly or entirely hide from you, which makes it fun to watch.
Hope this answers your question.