I also prefer to buy Bitcoin that way as I can be sure that my seller will really transfer the Bitcoin I am buying to my Bitcoin wallet. However, it is always good thing to know that we now have many choices as far as Bitcoin is concerned.
But what if your friend doesn't have bitcoins or doesn't want to sell right now? Then you have to resort to other modes like this. If not, will you buy from other members here and there have been increasing number of bitcoin scams also in exchange section nowadays. (Like that one who said he got hacked and the hacker scammed 1.5BTC because of the account).