Best practices around using BufferedBitmap instances?

I'm (slowly!) learning my way through the creation of a Watchface.  I'm thankful to have the Crystal watchface source to look at actual working code.  While the documentation isn't bad, real-world code helps tremendously.  I'm trying to understand the best practices around using BufferedBitmaps.  Are there any guidelines anywhere about the do's and don'ts in using BufferedBitmap instances?