Defining environment variables with launchd/launchctl

There are different solutions regarding the definition of environment variables that are stored in the launchd process, namely over at [StackOverflow](https://stackoverflow.com/questions/135688/setting-environment-variables-in-os-x) and [Superuser](https://superuser.com/questions/476752/setting-environment-variables-in-os-x-for-gui-applications) . How do these solutions differ?