Bouncing off a comment by Rob about his dilemma of realism versus Impressionism (which I interpret in this context to mean realism vs painterly approaches to painting style) I happened on this 10 minute video by Fogarty.
She uses a limited palette and her work comprises muted foggy interiors or exterior architecture.
There are two takeaways in her video relating to edges. In paraphrase she found the brush too soft and the knife too hard for constructing the required edge variation. Karen then used strips of matting board as a soft knife and used these to good effect in forming quite a range of soft edge characteristics.
This is a technique that offers some potential in landscapes and for still life and portraiture backgrounds.