Home and work are very "special" cases in that it's someplace most people regularly go to and from. So the app sends you personalized driving alerts/reminders, traffic updates, etc. There are definitely reasons for it, it's just not worth it to some. Others just have no idea that some of these nice goodies are helpful and not eerie and "privacy invading". So what if Google knows where I live and work? Frankly, that's something the government should know anyways, and it's failing abysmally judging by the amount of crime it's missing.