The ruling on licking the bowl and whether it is recommended not to eat to fullness?

Question:
Is it better to leave some in the bowl until he is full, or otherwise...?

Answer:
It depends; he eats from the sides until it is finished.
Q: Many people leave half the bowl uneaten?
A: He eats from it until he is full, and if there is some left, he leaves a little; it is better not to be completely full. The hadith says: It is recommended to leave some room for breath and drink. Good.
Q: Even if the food has spoiled...?
A: The remainder should be given in charity to the poor, or given to the animals.
Q: Scholars have discovered in the hadith that the last food one wipes off with his hand helps digest the meal... if he licks his hand, the oils that come out of the hand help with digestion?
A: Allah knows best. It is a sunnah (recommended practice), and that is all. The sunnah is to lick one's hand, whether it aids digestion or not. The sunnah is to lick one's hand; it is not your concern whether it aids digestion or not.