Excerpted from Bensky:  Chinese Herbal Medicine Materia Medica, 3rd ed.

• Fortifies the Kidney and Spleen yang, warms the Heart yang and fortifies the yang:  for a wide variety of problems due to insufficiency of Kidney yang and waning of the gate of vitality.  Common manifestations include aversion to cold, cold limbs, weak back, impotence, and urinary frequency.  Also for waning of the Spleen and Kidney yang with abdominal pain and cold, reduced appetite, and diarrhea.  It is also important for wheezing due to the failure of the Kidneys to grasp the qi.  In addition, an important herb for warming the Heart yang, particularly when deficiency of Heart yang is the etiology of chest painful obstruction.*
• Disperses deep cold, warms the channels, unblocks the channels and vessels, and alleviates pain:  for deep cold causing qi stagnation or blood stasis.  Associated problems include cold in the blood causing amenorrhea or dysmenorrhea, cold-damp painful obstruction, yin-type boils (chronic sores that are usuallly concave and ooze a clear fluid), and sores or abscesses that do not heal.  It enters the blood aspect and is often used in small amounts to enhance the blood-moving action of other substances.
• Leads the fire back to its source:  the principal herb for treating the upward-floating of deficiency yang.  Manifestations include flushed face, wheezing, severe sweating (when the sweat pours out like oil), weak and cold lower extremities, and a deficient and rootless pulse.  This pattern is called false heat and true cold, or heat above/cold below.  Also used for other conditions where the upper part of the body is hot (e.g., dry mouth, sore throat, or toothache that worsen at night) and the lower part is cold (e.g, lower back pain, cold lower extremities, diarrhea, weakness in the proximal position of the pulse).*
• Encourages the generation of qi and blood: with qi and blood tonics as an auxiliary herb for chronic deficiency of qi and  blood.*

Rou Gui - Cinnamomi Cortex