So you just spent some time on your brow weights, getting your spans to flow in a nice appealing smooth shape. Congratulations! Now let's mouse over the below image to see how it holds up in the opposite position.
Gross. It doesn't hold up at all. What was smooth in the down pose, is now jagged in the up pose.
In order for the emotions of the character to read clearly the brows should flow as a cohesive unit, giving us a soft arc when the brows are up and a bold straight when the brows are down. Take a look at these drawings of Aladdin to see examples of bold and clean brow shapes.
This all boils down to how clean our default mesh is. The more even and clean our edge flow is in the default state, the better chance it has of holding up in all poses. We are talking very small positional changes that have the potential to create very large and very noticeable improvements in our rigs. Once our mesh is cleaned up, we will even see that smoothing weights is a bit more predictable and useful.
Below is a version of the mesh cleaned up in it's initial state, an how that now plays well with our two poses.
Now obviously we can't have every edge smoothed out and evenly spaced; our models would become mushy and bland. In a later post I will go into how we need to be mindful of vertex speed when adjusting influences and how skinning workflows should involve setting key-frames.