well to help Lucid explain it, basically for a typical walk cycle animation, for example like this one;,
If, we look at the top row, there's 6 frames to depict the "walking towards right animation"
Since every frame is a 'unique' piece of drawing, each will consume it's own space (ram or harddisk). If each is let's say 6 mb (not so big, just for comparison), the whole Walking "walking towards right animation"
will take up to 6 x 6 = 36 mb, just for one animation!!
So if you need alot of animations, like jump and walk and run, the total of the space the animation will take will be enormous! And that's just for one character.
Lucid's Spriter basically solves this issues by instead of loading each unique frame of animation, the software and plugin will give each image a "Path" so to say, that it will follow. And this "Path" is much much lighter in size compared to traditional method.
Hope this help explain a little.