When plants begin absorbing the greatest proportion of their nutrition as microbial metabolites they become incredibly energy efficient and much lower levels of their energy are required to form cell compounds. The surplus of energy created at this level of plant health (level three on the plant health pyramid) is stored in the form of lipids: plant fats and oils.
When an animal is supplied with more energy than it requires for its own metabolism, it will begin to store the surplus energy in the form of fat. Plants do exactly the same thing. They store excess energy in the form of lipid compounds that can be metabolized in the future future if needed.
Plants will always maintain a minimum level of lipids needed to form cell membranes. As the energy surplus is stored, the lipid levels in many plants can increase as much as 3-4 times or more over the levels which are common today.
These elevated lipid levels serve as a backup energy battery and provide a tremendous buffer to environmental plant stress. When there is an extended period of cloudy weather with limited photosynthesis, the stored oils can provide additional energy and keep the plant from switching to proteolysis mode and beginning to degrade proteins.