The big difference here is that everything in public is… well public. resources aren’t. What you put in where is up to you.
Generally you would have everything the browser needs to access directly in the public directory. Which usually means: JavaScript, CSS, images, maybe some videos or audio files.
resources/assets is meant for things that have to be compiled or minified first. So you would have a few LESS or SASS files in resources/assets and they would get compiled and minified into one CSS file that’s put in the public directory.