His is the most effective guidance, as it preserves the health, completes satisfaction, and acquires the goals that this activity was meant to achieve.
Sexual intercourse was meant to achieve three essential goals: (1) Reproduction and the preservation of mankind until the number of souls that Allaah has ordered to come to this world is fulfilled and completed. (2) Expelling the water (semen), which would cause harm if it remains inside the body. (3) Satisfying sexual desire and enjoying sex and the bounty it represents.
The last essential goal is the only one that will be satisfied in Paradise, because there will be no reproduction in Paradise nor accumulation of sperm that needs to be discarded.
The best doctors state that sex is one of the best methods to preserve good health. Galinus said, "The essence of the sperm consists of heat and air, and it is hot and wet because it is produced from the blood that feeds the essential organs."
If this is how significant sperm is, one should realize that it should not be used or spent except to achieve production or to legally rid the body of it when it gets old. When the sperm is congested in the body, it will cause certain ailments such as obsession, madness and epilepsy. Discarding it, on the other hand, helps cure many of these ailments. This is why sperm is discarded from the body naturally.
Some of our Salaf (radiyallaahu anhum) said, "Man should take care of three things; He should not ignore walking, so that when he needs it one day he is able to do it. He shouldn't refrain from eating, because the intestines will shrink. He should not refrain from sexual activity, because if the wells' water is not drawn out, it will drain."
Muhammad bin Zakariyyah said, "Whoever ignores sex for a long time, his nerves will weaken, and their flowing will be blocked and his penis will shrink. I have seen some people who did not have sex claiming to observe some kind of abstinence and their bodies became colder, their movements restricted and unexplainable depression touched them. Further, their appetite and digestive powers also decreased."
Sexual activity helps lower the gaze, repulse lust, allows one the ability to refrain from illegal sexual activity and also achieves these goals for the wife. When one uses his sperm in a legal manner, he will benefit himself and his wife in this life and the next.
This is why the Prophet (sallallaahu alayhi wa sallam) used to fulfill his legal sexual desire, as he used to say:
"I was made to like women and perfume from your world."
Further, he (sallallaahu alayhi wa sallam) encouraged his nation to marry.
"Get married, because I will compete by your numbers with the other nations."
Also, Ibn 'Abbaas (radiyallaahu anhumaa) said, "The best of this nation are those who have the largest number of wives (up to four)."
The Prophet (sallallaahu 'alayhi wa sallam) also said,
"I marry women, eat meat, sleep, stand in Qiyaam, fast and break my fast. Whoever ignores my Sunnah is not from my people."
Further more, he (sallallaahu 'alaihi wa sallam) said:
"O young men! Whoever can afford it should get married, because it helps lower the gaze and protects the sexual organ. Those who cannot afford it should fast, because fasting will cure them."
Source: "The Prophets' Guidance on Sexual Activity" Taken from Healing with the Medicine of the Prophet (sallallaahu 'alaihi wa sallam) By Imaam Ibn al-Qayyim al Jawziyyah (rahimahullaah) - pp: 222 - 223