I've had my old school SPOT for about 10 years.  I finally have trained myself to remember to turn it on when I hit camp, set it out and check it occasionally to see if it has sent its OK.  It has always been reliable.  I also discovered last year that it will send a message from inside my tent if it has a clear shot through the screen toward the open sky.  My family appreciates the contact but last trip son Dan said unless he sees a help or 911 notification he doesn't pay much attention to if I checked in or not.  :-?  The OS version has two blinking lights when it is sending and just one blinking light once it has sent the coordinates which makes it easy to know if/when the message has been sent.
I used to have the tracking feature, but never really used it so cancelled that this year.  I do like the map I have on "file" when I return of my check in points and can copy it off the web and put it in with my trip report if I want to.  I do not carry a watch so I am also interested in knowing when I stopped for the night or started in the morning once I am home and can read the details.
I think the usefulness of sending a daily SPOT signal is that should I quit sending a signal and people are worried about me, they will have a general idea of where I last was and would probably begin in that area to try to find me. 
My directions regarding the meaning of "help" is that I am not in mortal danger but I cannot get out on my own and if I was in serious medical trouble I would hit the 911 option.