I usually have 4 right before I start a long training run and supplement as needed during the run. They're not incredibly high in calories, but obviously you don't want to eat too many and defeat the purpose of your workout/run.
Before and during to help keep you going. They are a nice alternative to gels which can be messy I use these when running more than one hour. Best taken 15 minutes prior to and then every 30-45 min during the run. Each pack is a serving or you can just use what you need. Great tasting as well!