The computer in your pocket deserves the same respect as any other. A simple password to access it will block the the same person that you invite into your house and use your bathroom with permission while you expect them to to not look in your medicine cabinet. Even worse, you can loose that phone. If you do not safeguard the location of your phone, consider having a second phone on occasion and use call forwarding, Do not save anything you do not wish to share on your person. Security in layers must be applied to smartphone usage behavior and if you don't know a little about that, consider asking a technical person that does. If a person has access to your smartphone and you have unprotected access to your email, it will take seconds for them to browse your email accounts that are not even associated with your phone. I am not paranoid, but you must consider that loss of your phone may grant access to any email or accounts that that you access regularly with your phone.
This is not news, but the limits related to abusing this ability have not been fully tested in the courts and I don't want to be the test case.