the 'pose to pose' animation style stems from 2d conventional animation. poses would be made, and other animators called 'inbetweeners' would draw the frames that went between those two key poses.

straight-forward animation is also ok, but you can tend to get yourself into a jam more often. you can use either way you like, but i prefer pose-to-pose, as it lets you get a sense of timing (from one still pose to another) before you go put in the details of the animation. that way if something seems to not have enough time to make a certain motion or too much time, you can change the frame the pose hits on more easily than if you animated straight forward and had to move lots of keys on lots of objects and lots of different frames.