that you can legally work and travel while waiting for your case to be decided. You don't have to be in any other status. However, keeping in mind, that should your 485 be denied, you have to leave immediately and if INS choose, they can put you in removal proceedings to have you deported (doubt this will happen though).
If you have maintained your status, such as H1, then even when your 485 is denied, you can still stay using your H1 status. That is the difference of having a separate valid status while in AOS--you have a backup.