The MACD indicator problem (like in any other trend indicator) is the periods when the market move sideway. So, for profitable system you can use this indicator only 0.33-0.5 of the time.
Technical analysis works because many people use it, and successful traders are able to predict how other people will react when they implement different technical analysis strategies; i.e. while the losers use TA to determine their trades (usually the wrong way), the professional traders wins...