All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Among the benefits that the wife gets when she answers the request of her husband to bed is that she fulfils a religious obligation. The Prophet informed us that if a wife refuses when her husband asks her to bed, the angels curse her. [Al-Bukhari and Muslim]
Among other benefits is that she fulfils the need of her husband (sexually) and fulfils her own need as well, which blocks the way of the devil in trying to lure people to commit illegal sexual intercourse. In addition to this, Allaah may bless you with a child who would be a support to you in this life and a stored treasure in the Hereafter.
To conclude, there are many benefits in a wife answering the call of her husband to bed, and Allaah rewards her for fulfilling her religious obligation.
As regards the type of this reward, then it is only Allaah who knows it, it may be by raising her rank in Paradise, multiplying her rewards, or it might be that the reward is by wiping out her sins, and it may be by both.
For more benefit, please refer to Fatwa 86279.
Allaah Knows best.