Always good to have at 2 bikes. Stuff can go wrong with your main bike, so you should have an extra bike at hand ready to take over when your main bike is being repaired. You might have someone visit you and it would be nice to have a bike for that person too. Or when its winter and too snowy and icy you might not want to beat up your main bike or constantly install and reinstall winter tires, so a winter bike is another reason to have a second bike.