So you post on Superbowl sunday morning... don't get a response less than 24 hours later and... and get annoyed?

Learn patience. You will need to learn patience if you want to animate.
First, you can animate layers using bones. This is VERY useful. Binding layers to bones is the same as animating the layers directly (except for z translation and uniform scaling).
A switch layer does two things:
It can "switch" from one layer to the next in "step" or "hold" interpolation. This means there is no smooth transition from one layer to the next.
Or it can use "interpolation" to "morph" from one VECTOR layer to the next but ONLY if the layers have the exact same number of points in the same place in the order they were created. Usually this is done by layer duplication and changing the duplicate layer.
Having said all that the trick is what is this good for?
Switching hand shapes
Lip sync
Head turns:
("morph" from a front to a 3/4 view)
Animating shape order:
(identical layers with shapes in a different stacking order)
Scene changes or camera cuts:
(Put two completed animated scenes in a switch layer. Switch between them to "simulate" a camera cut. For instance cutting between two characters during a conversation)
Switch layers are limited. They don't have any interpolation options except linear. This is bad. You can't do much with linear interpolation. it looks "flat", mechanical and unexciting. Interpolating from one vector layer to the next is also "linear". You can't morph a bent leg to a straight leg. The shapes are so different that it will just look weird. You would end up having to use a few extra layers to achieve a good result which is probably simpler to do with bones and/or point motion and actions on just one layer.
Originally switch layers were only intended for simple things like lip sync or hands, basic switching of layers. When I first signed onto this forum over two years ago... or more... can't remember now, a brand new exciting cool technique was just catching on. A "Moho" user was using a switch layer to do head turns!
This was exciting. Now... it's old hat and people have moved on to other cool things to "turn heads" (pun intended

) Another technique at that time (that hasn't seemed to maintained popularity) is using z-depth for turning heads. Elements of the face at different z values. When the layer or camera turns, the face appears to "rotate". This would be used for "subtle" turns.
Switch layers could be used to animate a character by setting up several different "step" interpolated layers of different versions of the character. Maybe you have one switch layer with two bone layers inside, each containing a different version of the character (front, 3/4, side, etc.) You can switch between them but they won't "morph" smoothly.
Using switch layers is not an animation "technique" by itself. It probably wouldn't be a good idea to use it exclusively. It is a tool that can aid in the animation process. It could be used to do one thing in one scene, or to solve a specific challenge. Changing hands for instance. Some people use multiple hand shapes in a switch and then change them (step interpolation. Smooth interpolation with vector layers won't work with hands very well). There is a technique (new technique mind you. With in the last year or so) that uses bones on a switch layer for say, a leg. A leg may turn and have a different shape but the bones don't line up. Have a second set of bones for the other layer, use bone offset so they don't overlap.
I use bones, constraints and custom scripting to do turns now. I still use switches to do "shape ordering" for hands. Two identical switch layers with the order of the shapes "flipped" can turn a hand from facing front to facing back very easily and uses bones for posing.
A lot of the "techniques" and "tricks" that seem to have been around for ages are brand spanking new... the only reference that exists for them is to search the forum (like I did to find the "head turn" switch layer trick when I first signed up).
I haven't read that new book that is out yet, but I would bet a lot of these "taken for granted" techniques would be in there.
-vern