A lot of brewing involves moving hot liquids around. That can be done by opening up a spigot, starting a siphon, or using a pump. The pump is the only thing that can move the beer vertically up, and it can also be much safer and less back-breaking than the other options.

This pump from chugger has all of the important parts (ones that touch beer) made out of stainless steel, so it is heat-tolerant and easy to keep sterile.