The first is the purification of the heart, the illumination of the natural dispostion and the sharpening of one`s insight.(According to Ghazali satiety(overeating) engenders stupidity and blindness in the heart).
The second benefit is a softness and purity of the heart, by which it is readied to attain the delight of
intimate discourse with God and to be affected by His remembrance.
The third benefit lies in mortification and abasement, and the removal of exultation, rejoicing and exuberance, which comprise the beginning of rebellion and heedlessness.
The fourth benefit is that one comes never to forget God`s trials and torments, or those who are afflicted by them. For the man sated is liable to forget those people who are hungry, and to forget hunger itself.
The fifth and greatest benefit lies in the breaking of all one`s desires for sin and in achieving mastery over the soul which commands evil. According to Ghazali all sins originate in one`s desires and strength and when the source of that strength is cut off meaning one starts eating less then the desires become weak.
The sixth benefit consists in the repulsion of sleep and acquiring the ability to remain awake for long periods. A man who eats his fill will drink abundantly and whoever drinks abundantly will sleep abundantly also.
The seventh benefit is that lengthy acts of worship are made easier. (He goes on to explain how food makes one lazy and the time that is taken in eating and preparing the food can be spent in worshipping much more)
The eight benefit is the bodily health which results from eating little. Again simple and something we over-look way too much on how eating less is much healthier etc etc and saves us from various diseases.
The ninth benefit lies in reduced expenditure. Whoever becomes used to eating little will find a modest income sufficent, whereas a man who is habituated to eating his fill will find that his belly becomes a creditor impossible to shake off, who seizes him by the throat every day saying `What will you eat today`.
The tenth benefit is that the aspirant is enabled to put others before himself and to give in charity to the orphans and the poor that which is surplus to his wants.
He goes on to explain each benefit in length giving some great narrations as always to back his points up. Just summarized these so I dont forget them.
