1) It lowers your profitability as you're forced to be very conservative on your position sizing (0.01 all the time). If you got a true edge, you're wasting it because of this.
2) If you always use the same lot dimensions, it'll be hard to equalize your wins and loses due to the shing spread, pip distance (unless you use a grid).
3) Your risk is obviously hidden, you got a illusion of security, but as soon as you begin getting many losses on a row or your own margin begins to dissapear you begin to sweat, and it sucks.
4) It is the easiest way to dismiss any account, even if the egy is perfect, your net conection, or the broker, or the spread widening, the news, whatever else is outside to acquire YOUR RECOVERY TRADES and sunk you in the deepest DD.