Write in private
Writing is a great way of clarifying thinking, forcing assumptions to be formalized which may have been unrealized, or held "informally" in some amorphous, imprecise, or incorrect fashion.
Write in public
Writing is a great way to be discovered by other people interested in a topic, make friends, and secure opportunitites.
Everything in moderation, including LLMs
Large Language Models (LLMs) are useful aides for lots of things, including learning and writing. However, generating writing on a topic is a very different learning experience to writing about it yourself.