There are certain opening lines which, although perfectly playable objectively, score much more heavily for one side or the other in practice. One such as the Exchange QGD, especially the Minority Attack. It is a fascinating structure, and I very much enjoy seeing Black handle it well, but in practice, White scores very heavily. The problem is that Black’s game is just much harder to play. White can afford several inaccuracies and still just be equal, but Black only has to play one sub-optimal move, and already he starts really suffering. It is an especially inadvisable line to defend against a stronger player, as Black usually needs to create tactical chances on the kingside. When White is stronger than his opponent, he will usually be able to keep a lid on such counterplay, and then Black’s queenside weaknesses will tell. As a result, I cannot really recommend playing the black side of this to the average player.
A typical example is the following game, which I witnessed at this year’s Hastings Masters. Black, an experienced 2200+ player, gets a particularly favourable variation of the structure, with the light-squared bishops off the board, and is at least equal for the first 25 moves or so. But once his kingside play stalls, he is soon left facing a lost cause on the other wing. Keith Arkell is the very last player against whom I would recommend defending such a variation – I don’t know how many houses he has furnished over the years, on the proceeds of the Minority Attack, but it must amount to an entire housing estate by now.