For others who might be as confused as me:

GNU Unifont is a bitmap font. It provides a fixed glyph for every code point in the BMP. It also covers additional code points in other planes.

I am guessing this is useful for writing editors that can edit Unicode text without knowing anything about various languages and their conventions. Authors who try to use this font to compose documents in (say) devanagari will have to learn the Unicode characters "in the raw", because I don't see a shaper for devanagari, so they won't get feedback that looks like real text.

If anyone can explain this better, please do!