What is the need of staging folder in Cordova 3.5.0 iOS application?

I had the same problem understanding the relation of /www and /platforms/ios/www. I realized the former should contain the source common to all platforms and the latter should hold platform specific modifications. The Staging folder appearing in the Xcode project is a link to the latter folder. Modifying the content on the former folder and running the app seemed to have no effect - no modifications were seen.

The thing I was missing was that after the modifications I would still need to do the build on command line:

cordova build ios

After that the modifications in the common folder are copied to the platform specific folder(s) and running the project in Xcode shows the modified content.

Sorry, I did not understand your question. Staging is simply a link folder to the ios-proj/www folder, and you can edit your code normally modifying the original.

In a multi-platform project "cordova platform add " will create a different project for each platform, in this case your editing should be done in the common code and sync sources through "cordova build" that will copy and compile code.

A similar question about the staging purpose: Purpose of Staging folder in PhoneGap 3.4? Only changes to index.html in this folder get recognized?