>>5805220These edges are softer than you think. It takes a surprisingly little amount of softening in an edge to get the effect of a soft edge. Also, creating a soft edge can be done in more ways than a simple gradient: texturing an edge softens it, shapes close in color are automatically perceived as having softer edges, and an area between shapes that's colored as something between those shapes counts even if its transitions are sharp.
For both soft and hard edges it's easy to pinpoint where they are, only lost edges are actually ambiguous. From there, an edge of any softness or texture is automatically soft, and one without either is hard.
The thing is that the only use artists have for edges is heightening the effects of perception. A painting done to physical accuracy won't be too different from a photograph, but in both cases a human will perceive the edges between darker things to be softer than those between lighter things. As a painter you have the option of embedding this perception into an image. Thankfully there are images in this thread so I won't need to post examples;
>>5804447 has harder edges in the light and softer edges in the dark.
However, since hard edges go hand in hand with illumination and therefore visual accuracy, both soft and lost edges are completely optional for good visual design. There's a school of artistry that maintains that images should only have hard edges. Hard edges are easier to design with, and limiting the kinds of edges brings forth similar visually interesting effects as limiting the available colors, textures or shapes.
All in all, if you know the look you want to make, go for it. But edges really are fundamental to picture making, whether you use every kind or not. What you want is an ability to recognize and correct a mistake when it has to do with edges.
