The game loads local files, so you don't have to publish your own mods when testing.
Publish local puts the packaged mod in Documents/Larian Studios/Divinity Original Sin 2/Local Mods for people who want to upload the mod to Nexus/etc. instead of Steam.
Question: do I have to send the levels I create to my friends who will play GM mode with me, or will the game download them to each client on its own?