The tied partner is usually stimulated repeatedly without relief. By carefully varying the intensity of stimulation, the passive partner is held in this highly-aroused state near orgasm. The tied partner's urge to orgasm can become overwhelming.
If the tied partner is allowed to climax it may be stronger than usual due to the increased tension and arousal that builds up during the extended stimulation.
The tied partner may also instead be denied orgasm or be given a ruined orgasm in which case they will generally feel strong feelings of sexual frustration.