A Read-only Buffer

The asterisk is for the situation when the current buffer is a read-only buffer—a buffer that cannot be modified. If insert-buffer is called when the current buffer is read-only, a message to this effect is printed in the echo area and the terminal may beep or blink at you; you will not be permitted to insert anything into current buffer. The asterisk does not need to be followed by a newline to separate it from the next argument.