Password allows for reading email in Landscape mode on the PreThis article contains unofficial information.
Once the code is entered, you will be able to turn your Pre while in message listing mode or while viewing a specific email and be able to read what is on the screen in Landscape mode. When turning the phone to this position, you will lose the menu, similar to when using the browser. Unlike the browser, while on it's side to read email, you will not be able to scroll using the gesture area.
Using the password does not make any permanent change to the Pre and you will have to reenter the password and start all over again the next time you want to read your email in Landscape. To make it permanent, follow the directions at the source link. Let us know how this code is working for you.
source: predevwiki via precentral