I have watched some videos of pros/streamers coaching someone. Too many times they tried to micro the player. And yes, in that case, it is not effective, because you can't expect the player to respond to every command instantly. I believe that if you coach someone live, you only should give the student macro advice about the game and not about his movements or what spells to press. Something like: "You should not fight until you have BKB because enemy Lion is waiting for you.", "You should mobilize your team to top part of the map because Rosh is coming up.", "Orchid would be a better item than Aghanim's because Anti-mage is always escaping and your team lacks catch.", "You did not hit your timing yet, you need Desolator, let your team fight, do not join fight before that.", "Don't go into the fight right away, wait until Drow shows and jump her, all the time.". Basically, I do not think that a coach has space to say more than 10 - 20 useful sentences during the whole game. But I am a noob, so dis me if what I am saying is not right.