Detail is a imperative to any well-finished rendering. If overdone, however, detail can be a detraction. Too "busy" a rendering is bewildering, and its main purpose is smothered in a welter of minutia.
A talented artist recognizes this fundamental fact: what is left out of a rendering can be as significant as what is put-in.
Study of photography with a wide range of tonal value will help you understand how and where detail should be played down or limited. Notice its tendency to disappear in bright sunlight or dark shadow, how obvious it becomes in middle value areas, how much vegetation is massed together rather than seperation in isolated clumps. You will also learn much by examining the work of other illustrators