Painting and Sculpture are like two knives that sharpen eachother. The painter who sculpts comes to a greater understanding of 3-dimensionality.
As a sculptor who has recently taken up painting, my mental evolution has been interesting. Detail may be achieved very quickly in painting. Polish and detail is time consuming and laborious in sculpture. It is easy to stop short of polish and detail in sculpture due to the time element and perhaps a sculptor's patience. Some sculptures may take months or a year whereas a painting might take several weeks to several months.
I am confident in saying the experience of painting is pushing my sculpting to greater heights in terms of polish and detail.