Mountain biking is so much fun because of the variety of terrain and discovering the unexpected on a ride. If you are going out on a trail ride then this is exactly what you are after. But if you are going to ride in a race then the more you know the better, otherwise you may just not make it over that finish line.
On a road ride all you need to know is the distance and the expected amount of climbing and you will be able to pace yourself properly using some of your training rides as a benchmark. With a mountain bike race you will also need to consider the type of terrain. If you are on district roads, farm roads and smooth track then its going to mean an "easier" ride. However if the route has rocky tracks, tight singletrack, technical descents, loose climbs and steep up hills then you can be sure of a tough ride taking longer than you would expect. At the start it helps if you start with riders of similar ability and speed so that you can pace yourself. Once you are into the ride you can assess terrain first hand and review your speed and pace.
The route profile will also tell you where the major climbs are and how steep they are. This is vital info that you must use to pace your race and conserve your energy especially if you are expecting big climbs towards the end when you will be tired. Race routes will often be harder or at least seem harder than your training routes. That is because they also cater to fitter faster riders than you and you will be riding faster than normal so it becomes harder. So find out as much as you can but still go into it expecting the unexpected because being over confident can lead to real disappointment.
