Details need to still serve the whole painting. The larger an artwork is, the more neutral the colors can be and the tighter the value plan (grouping value and having value repeat as shown in the first videos of this series). If a detail is well painted but is the wrong value (jumps too much) the painting can get ruined and lack cohesion. This is of utmost importance in ocean art where there is a serene and peaceful feeling desired.
Make sure to step back often when creating larger art. Large art is a relative term... maybe a 16x20 feels big after doing smaller paintings. This painting was 36x48 and I took frequent breaks to look at the art in a mirror, step back, and see it small from a picture on my phone.
Working larger will teach you about cohesive values. You will also learn about conserving your 'punch' values (dark and light) for only the 1-2% highlights.