I seriously doubt that Ctrl-Alt-Del is “the most used key combination for Computers nowadays”. I doubt it even as the most used key combo on Windows machines.
Ctrl-Alt-Del is not used for rebooting computers anymore… not modern Windows-based systems and certainly not anything UNIX-, Linux-, or mainframe-based.
It’s known as a Secure Attention Sequence, the point of which is so that a user pressing Ctrl-Alt-Del can be assured that the Windows operating system (rather than some other program) is responding to the key combination, and that it is therefore safe to enter a password.
Microsoft still likes users to make the Three Finger Salute for two things:
1. to bring up the logon prompt
2. to bring up a menu of options including: Lock this computer, Log off, Change password, and Start task manager.