Capturing errors and logs
Standard output is the cornerstone of observability. That's because one of the simplest things every application can do is to read information from standard input and print information to standard output. That's why the first thing every programmer learns is usually how to print "Hello world!"
Despite the fact that standard input and output are so important, users of modern software rarely know anything about their existence. Desktop applications usually aren't invoked from the terminal and users often interact with them using graphical interfaces instead.
Web-based software usually runs on remote servers and users interact with it using web browsers or custom client software. In both cases, standard input and output are hidden from the user.
But although users don't see standard output, that doesn't mean it does not exist. Standard output is often used for logging detailed information about internal application...