We are talking about H1 here. Who said all? If you don't have a valid H1 visa stamp on your passport, you can travel but you need to apply for visa to come back to the U.S. and if that's the case, sometimes they may not give the visa to you and consequently, you will be stuck in Nepal for life. In that scenario, if you have AP, you don't need to apply for visa to come back. However, when you come back, you will be in Parole status and then, you switch it back to H1.