according to the reference for the config.xml, pagezoom value can not go below 1.  In otherwords, it will not allow you to zoom out?
But there are scenarios where a zoom out is required.  For ex. displaying a webpage designed for 480pixel in a 240pixel device.Having the ability to zoom out would be a great help in this situation.
 
 
PageZoom
 
Sets the zoom factor of the page. Default zoom value is 1.0 (if unspecified). On Android, zero and negative values are not supported. On Windows, zoom value less than 1.0 reverts to 1.0 since lower values would not be readable. Page zoom settings will sometimes be reflected a few milliseconds after navigating from one page to another. A one-second delay should be anticipated. Not Supported when using Internet Explorer as the rendering engine.
 
Possible Values
 

Zoom factor of the page

Example