Traditionally, write access is allowed by default. However, as users become more conscious of various security risks, there is a trend to remove write access by default, at least for the primary login shell. To make sure your ttys are set the way you want them to be set, mesg should be executed in your login scripts.
The mesg utility silently exits with error status 2 if not executed on terminal. In this case execute mesg is pointless. The command line option --verbose forces mesg to print a warning in this situation. This behaviour has been introduced in version 2.33.
If no arguments are given, mesg shows the current message status on standard error output.