The first obvious use in outdoors is using it as a Fill Light...If "Key Light" (we discussed it earlier; in case of outdoor the Sunlight) is casting unwanted shadows; say Eye Sockets (when sun is high overhead) we can use flash as "Fill Light". We may use Grid or Snoot to limit the spread of flashgun
//youtu.be/http://www.youtube.com/watch?v=IzMcGCCEhiA
Fill Flash is must when you want to have sun in the back
//youtu.be/http://www.youtube.com/watch?v=jaBExauPQTo
Fill Flash is not just for portraits!
//youtu.be/http://www.youtube.com/watch?v=nKSGak4UGCE