Safe Boot or Safe Mode is used to diagnose the existing issues in MAC. Whenever the MAC produces some issues, It has to be diagnosed. In Safe Boot, It prevents some softwares from loading automatically. It actually makes the MAC to check the Startup volume. It does not load any unwanted kernel extensions. It loads only the needed kernel extensions to run MAC.
It doesn’t let it run any startup items or login items. It disables all the fonts which are installed by the user. When the MAC is in the Safe Boot, DVD player will not work, cannot use audio input or output devices and some of the other features. It disables hardware acceleration graphics. It is one of the common and necessary way to diagnose the issues. Here is a way to do so.
Shutdown the MAC, If not
Press the power button
Soon after hear the startup chime sound, Press and Hold the Shift key. It should not be held before the startup sound
Release the Shift key after the apple logo appears
Wait until the progress bar completes and bring you the login screen
To exit Safe Boot, Restart the MAC machine. It will bring back the normal mode to login.