Question re unit.dat files in VolcanoMan Mods

[76mm]

I've been looking at the mods for a couple of the East Front titles, including Budapest and Minsk, and noted that VolcanMan's mods for both of them seem to include McNamara DBs but empty unit.dat files.

What is the relationship between the unit.dat and OOB files, they seem to include much similar information, including attack/defence values, etc? Also, for these mods are we supposed to replace the existing unit.dat files with the empty ones, or what?