Quote - It's needed for owners of the French, Italian, Spanish and German versions of the original SWAT3 CQB. The data patch updates the map files in the these versions of the game in order to make them multiplayer-compatible with the European Elite Edition...without the map file update, crashes can occur in multiplayer games between European CQB and Elite Edition versions.

You can check the file in question yourself: if the Scenes.res file in the SWAT3 directory is 33806023 bytes in size, the update is needed.