Straight Ahead Action
Straight ahead action is so called because an animator literally works straight ahead from the first drawing in the scene. This process usually produces drawings and action that have a fresh and slightly zany look, because the whole process is kept very creative.
Straight ahead action is used for wild, scrambling actions where spontaneity is important.
In pose-to-pose animation, the animator plans his action, figuring out just what drawings will be needed to animate the scene. Pose-to-pose is used for animation that requires good acting, where poses and timing are important.
Relevance in CGI
Pose-to-pose action is an important tool in computer animation. Objects are built in a hierarchy, where each layer of the hierarchy has an associated transformation. Animation is then built up one transformation at a time from one pose to the next. For example, when animating a person walking, you would first set the pose position for the hips at the start of the motion, then you would adjust the hip translation for the end of the action. Then building upon this original pose, you would transform other objects in the model, until you had traversed the hierarchy.
All of your actions must be well thought out, and the timing and poses planned so that even in the early stages, the action is clear.