Is `controlling terminal` solely for user control?

I can kill processes and send signals to them with kill, so I don't need controlling terminal (or ctty) for that. So.. is the purpose of controlling terminal is solely for reacting to nudges from user? Transforming Ctrl-C key press into SIGINT ("hey, stop it!") and detecting if operator behind the keyboard is still alive ("keyboard is detached - SIGHUP, man")? [The docs](http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap11.html#tag_11_01_03) are full with details that doesn't answer the question "why it is here?", which must be obvious for everybody except me.