Straight Ahead
Straight ahead is just going forward with the movement as you are working, not through the use of key frames. The animator just does one drawing after another until the scene is completed. The use of straight ahead animation gives a great sense of spontaneity and creativity to the animation although it can be brought down by bad timing, less consistency and the storytelling can be lost.
Pose to Pose
Pose to pose is when the animation is planned out using key frames, which are the most important positions. The scene is completed with inbetweens to link key frames up. This method enables the animator to have more control over the movement and the final animation tends to have more clarity and strength. Other advantages are that timing is kept more effectively and the scene is easy to follow. However this technique can lose the spontaneity shown in straight ahead animation.
Example
Wallace and Gromit is a good example of straight ahead animation as the medium of puppets only allows you to use straight ahead animation as there is no chance of going back to previous frames.
Elise Townsend