our macMinis are full jenkins slaves. they used for:
1) testing (iOS/Android)
2) building both iOS and Android client
3) distributing iOS clients into HockeyApp and Android client into dropbox with sending emails with links
4) monitoring production environment
5) some other day to day needs
more info how connect slave to jenkins server
jenkins server itself does nothing accept WEB UI and giving orders to user tasks or schedule monitor scipts. it is actually running on some amazon machine and has disabled nodes.
this way is 100 times more convenient cause when your test code running on slave machine it can see itself simulators, devices and so on. thus some tasks that Appium can't do we can do in code - example add needed photo to Simulator and use it in test.