If the parent node shows the SUM of all its child's cost, you can better visualize the cost. And for the edge nodes, let's say I use the "cost" field to determ

If the parent node shows the SUM of all its child's cost, you can better visualize the cost. And for the edge nodes, let's say I use the "cost" field to determine the cognitive cost for any given task, I can more easily see which sub-task (edge) to prioritize if I want to get into "the zone" more quickly in an "intention"/project (parent node).