Rigid Binding
Flexors

For this tutorial, I'm going to explain how I use Rigid Binding on character animation, specifically, using flexors on joints.
So, here's my guy: Fig 1 Figure 1
Select the surfaces, then Shift select the skeleton. (For this demo, I'm just going to bend the arm, so I'm not worrying about the rest of the model. You'd probably want to select all your surfaces). Make sure that all your surfaces have had their Transformations Frozen and their history deleted (unless you have something depending on history or transformations - I find it easiest that these are all reset, though). Also make sure their normals are in the correct direction. (Fig 2) Figure 2
Animation : Skin > Bind Skin > Rigid Bind (In the options, Edit > Reset Settings)

Here's what happens when I bend the elbow and shoulder: Fig3

Figure 3
So, I go back to the bind pose, select the shoulder joint, and go to Deform > Edit Membership Tool.

I see this: Fig 4

Figure 4
The yellow vertices are being affected by the shoulder. As I don't need the affect of the shoulder to go that far, I'll CTRL click them to get them off the shoulder. I'll select one of the backbone joints and SHIFT click them to add these points to that joint instead.

I still get a ugly dent when I bend the shoulder: Fig 5

Figure 5
So, I'll select the points digging in there, and go to Window > General Editors > Component Editor. In the Component Editor, select the Joint Clusters tab, and scroll to the right until you find your selected vertices (I have 3 selected in the pic): Fig 6 Figure 6
So, in my case, I've got 3 vertices selected, attached to joint19cluster2 with a value(weight) of 1.0.

Select the 3 cells with the weight values, and pull the slider to the left until the vertices are in an acceptable position. (Fig 7)

Figure 7
As for the points up inside the armpit, it would take quite a long time to fix those this way, so I'll use a flexor. Go back to the bind pose and select the shoulder joint. Go to Skin > Edit Rigid Skin > Create Flexor.

This box will open: Fig 8

Figure 8
I'm going to go with an S,T,U of 4,4,4 and check the "Position the Flexor" box. I get the following: Fig 9 Figure 9
This is the flexor. Scale, Rotate, and Move it into an acceptable position. Bend the joint and see how it worked. It may take a few tries at different S,T,U values and weights to get it to work the way you want, but with practice, you start to get it pretty much on the first try. (Fig 10) Figure 10
Much better.
Michael McKinley