How do you decide what kind of edges your shapes will have? When do you decide, for that matter? Can you put off the moment when you have to commit to hard or soft?
You may have seen that it's not easy to convert a hard edge to a soft one. Once a stroke has dried it gets stubborn. Soft edges, on the other hand, can easily be made hard. Just let the paper dry and make a new stroke on top of the soft one.
Here's a painting by Trevor Chamberlain that uses almost exclusively soft edges.