No flash will replace a full-fledged studio lighting (although, in the studio with multiple external flashes, you can use the same lighting circuits). But it allows to obtain the correct flash-exposed shots with a lack of light in a sequential shooting - especially indoors.
It happens that after a lot of time spent to apply the right makeup, selection of colors, clothes and suitable background the result is not as good as expected. And it seems the camera was set up as it should, and interesting background is selected.
Sometimes real skills are found in the ability to break the rules, which follows the majority. For photos of it is the most actual in the portrait genre: the ability to go beyond the usual framework allows you to create truly memorable and unusual images.