see bigbud, topping is mainly about growing strong branches, it may be used to lower plant height but it is a damn extreme measure then. if you top a plant early on it is growing extremely wight and branchy. this won't happen in 6 days till flower so then it is only a measure to lower the plant if it is way too tall for flowering. it actually will lower the yield, in this case, on a well sized plant since it cuts the action taken will reduce sites for buds to grow on.