One can establish a perspective grid with ease. Fix three vanishing points for three sets of parallel lines respectively and the software will generate the grid for you. This makes subdividing a length trivial and much cleaner. In addition, the transformation tool can put a circle into perspective with ease: just distort the four corners of the bounding box into a cell of the perspective grid. If one sets up the division points on a circle before transforming, one gets the division in perspective trivially. (This works because the map of one-point projection to plane is affine, which maps lines to lines. With curvi-perspective, one may use mesh-transform.)
When the scene is more complicated, 3D software can take away much of the chore.
A large chunk of colour theory was about getting to know your paints and how to mix colour from your limited selection of paints. With digital software, you pick your colour. For example, it is easy to use the colour picker to pick a colour that is a little bit less saturated and a little bit darker than the previous colour.
However a new set of problems arises. One must know the limit of one's screen and how the colour profiles work.