GitHub provides the following features
Keep your local repository in sync by pulling changes from the Esri (master) repository. As the ArcGIS Runtime SDK for iOS team makes additions to the samples, you can easily pull them into your local version of the code.
Submit or track issues related to the samples (bugs, e.g.). You can get notifications for activity on issues you choose to follow.
Provide additions, updates, and improvements to the code via pull requests. One of the goals of GitHub is provide a collaborative environment, referred to as 'social coding'.
In addition to the ArcGIS Runtime SDK samples, the ArcGIS iOS team (within the Esri GitHub organization) makes available around a dozen public repositories that you can explore.
iOS tips and tricks
If you're interested in some awesome iOS tips, check out the tips-and-tricks-ios repository. The repo contains all the code for the popular Tips and Tricks Demo Threater at the UC 2013.
ArcGIS iOS projects
Additional code repositories are available from the ArcGIS iOS Team on GitHub. Here you will find code from technical sessions, demos, samples and presentations given at Esri events (such as the Developer Summit or Esri Users Conference, e.g.).