Question

What is the significance of the different length:volume ratios of the digestive organs?

Answer 1

The different length:volume combinations of the digestive organs are related to their function.
I assume you're asking about human physiology, so more specifically:
Mouths - We're omnivores, and our mouth reflects that with a combination of tooth shapes ranging from canines to molars. Digestion through mastication and exposure to saliva begins here. It's not very long or large in volume since it's dedicated to mixing and exposing the food to saliva rather than holding food.
Esophagus - The transit passage that allows our stomach to be further down, not so much for digestive reasons as much as allowing the respiratory and circulatory systems to have some room. It's very long but with lower volume since it's a 'passing-through' stage.
Stomach - More volume since food resides here for some time as it is acted on by all sorts of digestive juices.
Small intestine - It's a transitory passage that's also dedicated to nutrient extraction, so it is very long (more surface area means more absorption)
Large intestine - End of the line. Some water absorption occurs here, but because waste isn't headed anywhere (unless you're defecating), it doesn't need to be as long.