Edges in paintings can be Edgy i.e. by definition it can be an anxious, uneasy thing to do or it can be original and offbeat.  I was taught early on to paint shapes and not things.  That bothered me because for example I wanted to paint a tree.  I think now that painting shapes in the beginning of a painting is a good thing.  You can block in beautiful values and color in the beginning without being so concerned about things.  Some say a positive shape is an object like a tree and that usually is the subject matter where the negative shape is not.  To me it is more complicated than that.  That does not make me right.  Along the edge of a shape in regard to value there can be dark against light, light against dark, lost and defused edges.  Said another way there can be hard edges, soft edges and lost edges.  If you look at the painting titled: Shine On Me under the Still Life tab in this website you can see when you look at the outer edge of the pitcher shape light against dark, dark against light, defused edge and lost edge. You can also look under landscape on the website at the painting titled: Served Well and following along the edges of the farm equipment you may see hard edges, soft edges and lost edges. Edges can be uncomplicated, peaceful and wonderful or they can be complicated, edgy and wonderful too.  I pray that God guides our paint brushes to Glorify Him.