I have three sets of tires that I use depending on conditions. I put the set most suited for the day's race on the bike and use another of the sets for my pit wheels. My Trek XO1 came with Bontrager Jones CXR's which are general purpose. I have a set of Michelin Mud 2's for wet muddy conditions where the tire needs to cut through slop, and a set of Continental Speed's with the rasp tread for fast dry surfaces. The Mud 2's don't have any lugs on the side of the tire and can be unpredictable when riding across loose stone and off camber's but the ticket when it is really muddy and sloppy as the tire cuts through the slop down to hard ground. Last year in a race I fell two times while crossing a loose gravel driveway and twice on a dirt pathway with an off camber turn during a race while riding on the Mud 2's.
It only takes about 10 minutes to switch a set of tires on the wheels. I'd recommend that you get a set of tires for the different needs on the courses in the area you race. If you watch the sales at PBK you can pick up a set of tires for the price of one at your LBS. At your first race take a look to what the guys in the upper categories race and copy them. In the beginner classes many riders will use the tires that came with the bike and not a condition specific tire.