The Bible teaches us that sex is a good thing inside marriage, and that married couples should have a lot of sex. They should have sex whenever one of them desires to (I Cornthians 7:3,4). They should only abstain from sex for periods of time when they have both agreed to it ahead of time:
Do not deprive each other except perhaps by mutual consent and for a time, so that you may devote yourselves to prayer. Then come together again so that Satan will not tempt you because of your lack of self-control. (I Corinthians 7:5 NIV)
They should not abstain from sex for a time except by mutual consent, otherwise they are depriving each other of the intimate display of affection that they both deserve. It is, however, OK, to abstain from sex for a little while if they have both agreed on it for the sake of devoting themselves to prayer. This demonstrates that although they enjoy sex, they do not worship it. Nevertheless, abstaining from sex should never be normal within marriage, therefore, after the agreed upon time is over, they need to come together again in sexual intimacy. If they try to prolong their sex fast they run the risk that Satan will tempt them because of their lack of self-control. The husband will be tempted to seek sexual satisfaction from pornography or masturbation or perhaps even other woman: the wife too may be tempted to seek emotional support from other men. Therefore they need to limit the times that they are abstaining from sex. There is nothing holy, honorable, or noble about not having sex with your spouse.