The help for the BitmapData class says:

The BitmapData class lets you create arbitrarily sized transparent or opaque bitmap images and manipulate them in various ways at runtime.

This class lets you separate bitmap rendering operations from the Flash Player internal display updating routines. By manipulating a BitmapData object directly, you can create very complex images without incurring the per-frame overhead of constantly redrawing the content from vector data.
The bolding is mine, and it is what I would like to discuss. I apologize if this has been done to death, the search keeps timing out on me

Lets say I have a movieclip that is a series of image files (.jpgs or .gifs) with no vector data. Just a flipbook/sprite essentially with the different animations packaged together. If I take this movieclip and place it on the stage, is flash doing any unnecessary work that would be helped by using the BitmapData class? As you can tell, I don't know much about the class and am wondering if I should be learning it.

I don't think it will be much of a problem with my current project (being turn based and all), but I would like to be aware of better ways of doing things before I get into bad habits. The game is basically a tilebased game with movieclips thrown on a scrollable 'playfield' movieclip so the player can move and scroll it easily to plan, and the game engine can move and scroll it to highlight what is happening while the turn is playing out.