I have not faced that question in writing as an adult. If I have something that is worth writing up then I give it a try.
As a student, though, this issue affected me as it presumably has many others. How do you fill in a length-specific writing assignment when you have little to say? As a kid I wrote in big (handwritten-) font so that helped some. Beyond that I taxed what creativity I had at my disposal to fill in the prescribed blanks with something vaguely coherent. I never liked such assignments.