Movie clips are more convenient and easy to use, think of it as a pre-built PC shipping order instead of just a box of components you got to put together to use as in older packs with stickfigures with multiple parts.
With movieclips, you can first
A. Include multiple variants of the same stickfigure in one movieclip, and select different versions by changing the frame (Ex: 360 packs)
B. Break apart the movieclip to use a prebuilt stickfigure with many parts, already layered and assembled and ready for use.

Movieclips are save memory as well, using movieclip BGs helps you conserve memory usage in your animations iirc.