Most mammals chew, while reptiles on the other hand, seem to like only taking one bite. This is because chewing expends energy.
A 2013 study in PLoS One postulates that a major advantage for swallowing food whole is "No time needed for processing." Animals that swallow food whole get the energy from their food ASAP with minimal energy tax. The Plos One researchers think not chewing is what helped some dinosaurs grow so large!
In a study done with a python, 37 percent of all the energy in the food was spent just digesting it in the first place! So, many animals swallow their food whole, simply to get the energy as quickly as possible.
Seeker: Deep-Sea Dragonfish Predators Have a Freakishly Wide Bite
PLoS One: Evolution of a Functional Head Joint in Deep-Sea Fishes (Stomiidae)
Science Daily: The benefits of food processing: Processing food before eating likely played key role in human evolution