The beauty of it is that many of them will be heavily bet based on their performance in their last race. While most harness track surfaces are made to be hard and handle rain and snow well, some still show an advantage, or bias, when they are wet. A half mile of five eighths mile track that normally favors inside posts can turn on you and start to favor the mid posts. Get the stats on off track post position statistics and pay particular attention to that angle. If a horse gets a 45% advantage by being in post position five, that's a huge advantage over other posts.