1. They're annoying.
  2. No, seriously: they're really, really annoying.
  3. They're almost as annoying as people who think that using CAPS will make me more receptive to their message.
  4. The louder the transmission, the less substantial it's content. In other words: the more you scream, the dumber you appear to be. No need to advertize it: we'll figure it out soon enough.
  5. In the rare event that the above doesn't apply, either buy a pair of glasses or enlarge the base font on your device.