Even if you're out for a weekend game of soccer with your recreation league, an energy bar can help your performance.* Since your muscles are constantly using up its energy storage, the better you're able to replace glucose in the body, the more energy you've have for longer durations.
Energy bars come in a variety of different nutrient values, so regardless of your particular diet there's sure to be one that will suite to your needs. Energy bars are also great for people on the go, as they will provide a quick solution for times of need.
If you're using the energy bar as a meal replacement, try and find one that contains at least 10 grams of protein so that you'll get a slow the release of the nutrients and a steady level of energy from the bar.*