I don't think it's murky at all. The ME prefix limits events to being triggered only by your client (yourself).

This...
Code:
on ME:*:JOIN:#: {
  msg # Hello $+(#,!) How are you today?
}


is the same as this...
Code:
on *:JOIN:#: {
  if ($nick == $me) {
    msg # Hello $+(#,!) How are you today?
  }
}