They aren't outside of game mechanics, but using that you can get that the bog standard personal shield can take somewhere around 4-5 hits from a phaser before it is knocked down. They also have an auto regenerate function where they recover strength over time. Yes. It varies from light armor to some type of power armor. If you have man portable weapons that can take out modern armor what use would all that have? If you have a ship which can't be detected and can destroy all life on any planet in a single shot how does any of that matter?