I have seen many courses where a stake in the appropriate color was in the middle of the fairway. I always questioned the usage as well.
I didn’t question their usage, I find them quite useful when the contours and direction of the fairways makes it difficult to ascertain a target for your ball off the tee.
I recently played with a relatively new golfer who kept asking “where should I aim?” and I kept saying “the 150 yard marker”.