“Inferred” is the default setting for storyboards and it means the scene will show a navigation bar when it’s inside of a navigation controller, a tab bar when it’s inside of a tab bar controller, and so on. You could override these settings if you wanted to, but keep in mind they are here only to help you design your screens. The Simulated Metrics aren’t used during runtime, they’re just a visual design aid that shows what your screen will end up looking like.
"FreeForm" Usually you use the freeform property when you add the view controller as a child to another view controller programmatically and you really want to have that fixed size.If you push the view controller or you present it as modal view controller (and you use the modal presentation styles) then there is no need to use freeform.Also another use of the freeform property is to preview the actual size of your view controller when is presented as a modal view controller using existent presentation styles.
原文：http://www.cnblogs.com/tig666666/p/5953077.html