The Grignard doesn't add to anything, the net change is 0 if you look at the d3 synthon, it's become a carbon with a - charge on it.
Looking back, I may have misinterpreted what orgopete was saying. Pete, if you're suggesting that part of the importance is picking out the correct strategy (ie; what we're talking about with the Grignard needing to react first) then I agree. However, if you're suggesting it doesn't matter because the class is focused on single reaction transformations and all the poster needs to focus on is coverting the alkene to the aldehyde then I don't agree at all.