I looked into the use of flash kits in outdoor or out of studio locations and found that for most commercial photographers (wedding and event photographers) it is an essential piece of kit. It allows the photographer to still have control of the overall look and feel of the image, without having to rely on available light (sun light). It enables one to shoot on a cloudy day, at night or in low light conditions. It allows you to have both the background and foreground properly exposed if needed, for example shooting against the sky would either under expose the sky or your model/subject, but if you expose for the sky then light your model from the front, both will be properly exposed.
I've included some photographs that I liked as an example from http://www.prettygeeky.com/
The photos are almost dream-like with their vibrancy of colour. The first one features a baby and balloons outside on some grass. A flash seems to have been fired from just right of the camera, reflected in the balloons and creating a shadow silhouette on the babys face, and perhaps with an umbrella or softbox. The second one features a city at night and a lit up model in the foreground. The third is an outdoor shot of a model on grass, whose front is properly exposed but has a flash behind as well creating a rim of light along her shoulders and hairline.
https://www.youtube.com/watch?v=duWEjm6clRE
An interesting video showing an outdoor photo shoot of a band.