The Full Page feature toggles between two different zoom levels. When using Full Page, the point size of the display font is adjusted so that an entire page of text can appear on-screen at once.
Depending on the size of your monitor, Full Page view can be very useful when working with the general layout of the braille document.
The text is normally too small for editing, but may be useful for visually seeing where the pages break.
A check mark next to Full Page indicates that it is enabled. When not using Full Page, the screen font size is as set in Global: Fonts...