What is the purpose of applying a siphon to a cask on end?

Applying a siphon to a cask on end primarily serves to ensure proper sediment control while serving the beer. When a cask is filled and allowed to carbonate naturally, yeast and sediment can settle at the bottom. By positioning the cask on end and using a siphon, the beer can be drawn from the top, allowing the clearer liquid to be served while leaving the sediment undisturbed at the bottom. This practice helps maintain the beer's quality and clarity as it is served, preventing cloudiness and off-flavors that can arise from disturbing sediment.

The other options, while they may seem plausible, do not accurately capture the intention behind siphoning from a cask on end. For instance, while easier access or quality control might be considerations in some contexts, they are not the primary aim when it comes to managing sediment during pouring.