What does "Main Interface" in Xcode actually *do*?

Question

I'm moving some older projects to Xcode 4.5, and I'm a bit baffled as to the actual function of the Main Interface project dropdown. What does the framework actually do with that value?

Answer 1

beware if you have a storyboard based project. Editing the MAIN INTERFACE field manually is dangerous. If storyboard is not found it thinks you mean a NIB. will change the app to a NIB based project. Safer to choose a storyboard from the drop down.

BEFORE - i has a storyboard based project
UIMainStoryboardFile~ipad : Main_iPad
UIMainStoryboardFile      : Main_iPhone

I mistype the name in MAIN INTERFACE field to Main_iPhone1 I ran the app and it crashed as Main_iPhone1.storyboard doesnt exist I changed it back to Main_iPhone but project refused to build even after a lot of cleaning.

Casued by the key in the plist also changing along with the value

AFTER
UIMainStoryboardFile : Main_iPad
NSMainNibFile          : Main_iPhone1  <<project changes to NIB based

Changing Main_iPhone1 back to Main_iPhone only changed it from Main_iPhone1.xib to Main_iPhone.xib which doesnt exist and also crashes.