The most important factor when it comes to rigging is knowing the difference between IK & FK…
What is IK and FK?
IK (Inverse Kinematics) is a method of animating that reverses the direction of the chain manipulation.
Now when it comes to knowing the pros and cons of IK it requires great thought about how you will link your objects. Joints can be limited with specific positional and rotational properties. Position and orientation of parent objects are determined by the position and orientation of child objects.
With that being said, Inverse Kinematics is often easier to use and create than Forward Kinematics (FK)
Each animator should experiment and find what works best for themselves – DJ Nicke
Within FK (forward kinematics), you animate the hand’s position by starting at the shoulder, rotating it how you want, then moving to the elbow, rotating it how you want, and then going to the wrist, and rotating it how you want. The hand is not fixed to some point in space; its position is entirely determined by how you bend the arm, which you animate directly.
IK is very useful when it comes to positioning a character like putting it in a pose. (For example, if a person was resting their hand on a table while their body is facing away from the table; say 90 degrees, and I made the person turn towards the table and I didn’t want the hand to move).
With IK, I can achieve this with the broken hierarchy; I can move the body and the hand will remain stationary. If I use FK along with a mirror hierarchy, the hand will follow the body and not stay still. With IK you control the pose with the large plate shaped widgets at the hands and feet. While with FK, each bone from shoulder to wrist needs to be adjusted. This is exactly how bones can be moved correctly after creation.
Trying to use IK in more interesting ways to improve animation workflow – Evan Doody
Inverse Kinematics does all the challenging computational work of calculating what the pose is. In the Before State – Luis B
This reference really helps understanding what you can do with IK and or FK handles.
This other reference also helps to teach you to understand the difference between IK and FK. It also contain screenshots and GIFs on IK and FK handles in motion.
This is another great reference for learning about the uses with IK and FK. Complete with GIF animations including a video to show the potential of using IK and FK handles.