I have Photoshop CS6 and in the timeline panel's menu there's an option called optimize animation and it has two options: Bounding Box Redundant Pixel Removal I searched in the internet and Photoshop help but I didn't understand anything about them :| I'm not English so I'm sorry if I have any mistakes
"Bounding Box" is the smallest rectangle which can be drawn around an object so that everything that is part of the object is contained within the rectangle.
"Redundant" means "things that are not needed because they are repeated" (more or less). There is an old joke about a goverment's "Department of Redundancy Department".
An animation is 2 or more images shown in sequence.
So given an animation 100px x 100px of a 10px circle on a white background:
The "Bounding Box" optimization. Frame 1 is saved as a full frame (100x100; 1000 pixels); frame 2, the ball moves 2px right. A bounding box is calculated based upon the changed pixels, the size of the box is 10px x 12px. Frame 2 is saved as (10 x 12; 120 pixels) along with the position of the upper left corner for alignment. The two frames are 1120px of data, not 2000. A big storage savings.
The "Redundant Pixels" optimization. In the above example, frame 2 has a bounding box of (10 x 12 px) but the number of pixels actually different within that box is a lot fewer than the total 120px saved. The ones unchanged are redundant information between frames. In a GIF, transparency is usually a single color, if you mark all the unchanged pixels as this color instead, you wind up with large chains of pixels which are one value, which can then be easily compressed using, say RLE compression. Instead of 100 bytes (1 byte per pixel), you can store 2 bytes (1 byte = number of pixels; 1 byte = color index).
Both of these optimizations are file size and bandwidth optimizations. They aren't going to change the look of your animation.