When a clip instance on the stage is set as Display > Export as bitmap, it is rendered in very low quality.
The document quality setting (e.g. JPEG quality = 100) doesn't seem to affect the rendering.
I usually use this feature for (clips including) large bitmaps, so that they might be exported as smaller bitmaps (while keeping the whole resolution in the source file). The quality loss seems worse when the bitmap instance is heavily downsized on the stage, as if Animate was unable to make a proper interpolation from a larger bitmap.