Relay notifications or/and messages, and other useful functions, like automated control of your home server and other electronics like vacuum robot and such from places with bad connection, also automated fetch of information you need, like timesheet or news you follow or state of your home and this is just fraction of use cases the only limiter is your imagination

It’s very effective for sysadmins if you want to get real time notifications about server stats. The possibility are endless because you could push everything with curl from commandline or cron. For example why not get informations about SSH login attempts or CPU usage or unattended upgrade logs?