kext files (kernel extensions) and login scripts in the earlier Mac OS X versions would cause users plenty of a headache on Mac’s startup. Over time, broken login items searching for missing applications, start eating up more system resources. It may happen that the application uninstalled from Mac long ago, still loads on startup. They sneak into the list of login items and settle there, unnoticed, until Mac’s performance drops. Most apps don’t request user permission to launch at startup, so they silently run in the background.
Every time you start your Mac, services and apps known as login items launch concurrently with the system.
