In most bike races, when you get a flat it means trouble. For most of us, we don't race on a team with domestics that can come back and get us to bring us back into the pack. At the amateur level, even if you do have teammates they may not even know you have a flat.
Then worse, the vehicle "de depannage" may not even allow you to draft, so you have to time- trial you way back to the back. In many cases, that means the end of your race. And to make things worse, some spoon may decide to attack while you're changing your wheel.