Do bucket brigades really work? Or is it just an old idea that no one uses anymore?

The idea of the bucket brigade does actually work, but on a small scale. The concept of water putting out fire only works if there is enough water applied to overcome the BTU's being put off by the flame, otherwise it's instantly converted to steam and serves no purpose. Modern day fire tactics utilize 95-200 gallons per minute application rate to overcome BTU's being put off by the burning of modern synthetics. It's totally impractical that water from a hundred buckets being applied at once would work, let alone the small amount from a bucket brigade. If your trying to control the spread of a small fire, however it would work by wetting the material sorrounding the burn preventing spread but even then the application rate would still need to be high enough to outperform the flames (heat) of drying the water out faster than it could be applied.