For example, if you have IOS plugin with requires some flags or frameworks, libraries or pList values to be added in compiled IOS project, or you did your own plugin for your game, no need to add it manually every time. IOS Deploy plugin will do this for you on Unity building phase.
To specify additional Frameworks or Flags open Plugin settings window Window → IOS Deploy → Settings
The following screenshots will demonstrate how you can specify additional setting of XCode project with IOSDeploy Editor window:
Note: Extension si designed to work on OSX. If you will use Windows for building IOS project IOS deploy may not work.