While I'm not Roman Catholic, I do admire their stance on the importance of consummation of the marriage (having sexual intercourse after marriage.) It is so important in Roman Catholic theology where divorce is prohibited, that an unconsummated marriage can be dissolved by the Pope. And an inability or intentional refusal to consummate the marriage is probable grounds for an annulment. Roman Catholic canon law defines a marriage as consummated when the "spouses have performed between themselves in a human fashion a conjugal act which is suitable in itself for the procreation of offspring, to which marriage is ordered by its nature and by which the spouses become one flesh."
In our sexually-saturated culture, much of the church has foolishly lost the beauty and importance of sexual intercourse between husband and wife. Some Christians mistakenly believe sex is the result of the fall of man. Nothing is further from the truth. God instituted sexual relations between the husband and wife before the Fall (Gen 1:28) and pronounced it along with everything else He created as “very good” (Gen 1:31). In contrast to sexual immorality, when we engage in a God-sanctioned sexual experience with our spouse and become one through the act of sexual intercourse, we can actually glorify God through the experience (1 Cor 6:18-20). As John Piper's book "Sex and the Supremacy of Christ" so powerfully clarifies - our sexuality should glorify God and is designed by God as a way to know God in Christ more fully. Inviting Christ into your sexual appetite is an amazing journey. The misuse of our sexuality distorts our true knowledge of Christ and all misuses of our sexuality derive from us not having the true knowledge of Christ.
As I wrote earlier, sexual intercourse is not only a physical act, but also the powerful spiritual union of the man and woman. Sexual relations inevitably and fundamentally alter the relationship between a man and a woman; after this most intimate of acts and communication that can occur between two people, the two will never look at each other or be able to think about one another the same way again.
As important as consummation of the marriage is, it is just as important that sexual relations continue between the husband and wife for the duration of the marriage (barring physical injury or disease). Why? Think about this - the sacrament of Communion within the Body of Christ is important not only as a memorial of the Atonement, but a sign of continuing fellowship with the Church. To receive communion is to signify continuing oneness with the Body of Christ. Similarly, the act of sexual intercourse between husband and wife can rightly be considered the repeatable, ongoing demonstration of the continuing oneness of the husband and wife (1 Cor 6:16-17). This is why continuing sexual relations between the husband and wife is important. Just as it's not normal for a Christian to suddenly abstain from receiving Communion within the church, it is not normal for a physically-capable husband and wife to stop regular sexual intercourse. Sexual intercourse should continue throughout the life of their marriage.
While sex is clearly not the most important thing in marriage, neither can we say that it is of no importance. Scripture clearly affirms the importance of sexual relations within marriage (1 Cor 7:3-5) – ironically, this passage was penned by Paul, a celibate, as instruction to married couples. Barring physical reasons (i.e., injury, disease, etc.), a marriage where regular sexual relations has ceased is in trouble.
Because sexual intercourse is the intimate physical expression of the spiritual union between a husband and a wife, the sexual experience can and should actually intensify in pleasure through the years as the bond between the two of them deepens. Sexual intercourse between a husband and wife can actually be far more powerful and gloriously intense decades after marriage as the bond between them strengthens, than at the start of the marriage.