During the Golf Writers of America Championship in Myrtle Beach last April, Bill Daniels of Golf Chicago and I were left wondering just that question. On two holes, rakes left on the edges of bunkers kept his drives from going into the bunkers. The balls were right against the rakes and would have gone into the bunkers otherwise. “I always thought rakes should be placed in the bunkers, at least until what happened today,” he said. I agreed with him at the time, but hit a rake and went into a bunker later in the round and didn't think it was fair then.
I decided to go to the Decisions on The Rules of Golf to see what the United States Golf Association had to say about the matter. While admitting there is no perfect answer and that it is left up to the committee to decide where to place them, the USGA recommended putting them outside the bunkers, saying there is less likelihood of an advantage or disadvantage to the player.
One of the disadvantages of leaving the rakes in the bunkers is that it tends to stop a ball on the sides of bunkers instead of in the flat spots, resulting in a more difficult shots, especially in the smaller bunkers. Sometimes it may not be possible for a player to replace the ball in the same spot or find a spot that is not closer to the hole when his ball is against a rake on a slope. Remember, that there is no penalty involved if your ball happens to move when removing the rake. See Rule 24-1.
Another disadvantage to having them in the bunkers is that players have to walk out even further into the bunkers to get them sometimes and this results in them having to rake larger areas, which in turn slows down play. I've played at several courses where the rakes were placed on the back on golf carts. Not a bad idea at all. However, you have to be careful not to leave them in or near the bunkers as I did on several occasions. So it seems the best option is to put the rakes outside!