There are good and bad writers. I have my opinions on who falls into each category, and where I draw those lines. There are two anaolgies I want to use to highlight a simplistic point on where I make this distinction.
A skilled cobbler makes shoes that fit the feet, certainly not too large.
Jane Austen is the antithesis of that point. The best "cobblers" I can think of currently are Cormac McCarthy and Raymond Chandler, where not a word feels wasted.
In academic writing, this analogy is more appropriate.
When there is plenty of wine to go around, give as much to each man as he desires. If there is little, give every man equal portions.
If you are writing a book, there are pages to elaborate the points you find most important. In particular to this point I hate to read "This is beyond the scope of this book", which is rubbish in most cases, and could instead have a reference in place without patronising the users to assume they wouldn't understand a concept. In shorter essays, the point would be that if you only have 750 words, and need to make 3 points, it makes more sense to give 250 words to each point, and not 500 to one and skip over the others.