I feel like the “correct” answer is write exactly how much you need to answer the question well, but tbh that hasn’t been very useful advice for me in practice. You shouldn’t fill space with fluff just for the purpose of getting to the max length, but I think most of these prompts are deep and/or open ended enough that if continue thinking about the question, you should be able to come up with enough meaningful information to fill most of the space. I just figure that if you don’t that, other applicants will be taking full advantage of the space by including additional points, deeper self-reflection, etc.