It cuts both ways, as others have mentioned.

2 years ago we were meant to go to Hong Kong en route to a tour of China. The tour was in October. In March I spotted a fare anomaly, where an A class (First) return to HKG was priced LOWER than a D class (Business) fare (but higher than W). We booked two seats, but I was concerned that if my reservation was for A class, the price could be raised in the meantime. However, if I actually bought the tickets I would be covered (and A tickets are refundable). I did that, about 7 months before the flight, and even changed the dates about 5 times in the meantime. I was not surprised that by August EL AL had noticed the anomaly (I think a lot of people were taking advantage of it) and put up the price very significantly (I think by about $2000 for the round trip).

Of course, having actually issued the tickets and paid for them, we were covered, and nobody asked us to pay extra!