The reason people say 1200's can't coach is that they may learn their "bad" habits to other people. Also the analysis skills aren't that developed so you could talk about strategy but meanwhile missing all the tactics. This is for instance what happens when we look at the videos of Backyard Professor. He can tell us the strategic plans in a position but loses to simple tactics!
But I still think 1200 players can learn other players something about strategy still (: , strategy like controlling the centre, open file for rooks, piece development, pawn structure and king safety could be learned from a 1200 just as well!!
And even certain endgames can be learned from 1200, but often times if the student reaches 1200 he needs to learn from higher rated players so ultimately the 1200 player coaching is very temporary!
Divine has a point aniket