Unlike filtered and pasteurised lagers, some beers are meant to contain a bit of yeast in the keg. In some cases, a light dusting of yeast is added during the kegging process, allowing beers to carbonate and “condition” inside the keg. Furthermore, some beer styles are meant to be served with a nice visible dose of yeast in suspension, adding to their appearance and flavour profile. The process of flipping a keg throughout its journey can keep yeast distributed evenly, and prevent unsightly clumps forming that could otherwise make it into the glass.
Sometimes the orientation of a keg has nothing to do with preserving the beer inside. In some supply chains, upside-down kegs signify a keg that is empty and ready for collection. This is a simple way to separate ingoing vs outgoing kegs making life easier for delivery drivers.