Nokia Maps 3.09 - What is the difference between Maps voice files with street names and the other voice guidance files?

Maps voice guidance packs with street names use computer voices and allow the street names to be included in the navigation voice instructions (using "text to speech" feature). The voice packs with street names can be used with both the drive and walk navigation. With walk navigation the voice packs with street names are the only voice packs that can be selected.