Most of the essays you do for Academies or nomination applications have word or space limits. It is usually best to be brief and use as much shorthand as possible. The reader will understand the context, and knows what you are referring to if you say "academies". I know my son did essays for USMA, USNA, and USAFA, along with three MOC applications, and with each essay he asked me to help him rephrase parts so they would use less characters. It was a challenge usually to maintain substance and style, but with less words. Acronyms are a way to do that when possible.