The dopesheet provides you with a way of viewing and editing keyed animation. Similar to a cel animator's dopesheet, it shows your entire animated sequence, frame by frame. Because you can see your whole animation, you can accurately judge its overall motion and timing, allowing you to quickly block out the animation. Keyframes are easily identified on the tracks as colored boxes.
You can retime all or just segments of an animation in the dopesheet with a minimum amount of effort. For example, if you wanted to lengthen a 100-frame sequence to 200 frames, you would stretch (scale) the animation segment on the track to be 200 frames long.
You can modify your animation sequences by editing regions of keys on the tracks with standard operations such as moving, scaling, copying, cutting, and pasting. You can delete them, shift them left and right, scale them — all with or without a ripple.