In an ideal world, the only reason to have sex would be because we want to relieve sexual tension, we're attracted to our partner, and we want to strengthen our bond. But the real truth is that while some couples do it to become more intimate, others do it simply so they don't feel guilty about not having sex.

This was revealed in two recent studies conducted by the University of Toronto, which divided both the most common reasons why people have sex and the ones most relevant to long-term relationships into two categories of motivation: approach and avoidance.
Approach motives pursue a positive outcome. ("I want to increase intimacy with my spouse" or "I want to feel closer to my partner.") Avoidance motives aim to evade a negative outcome. ("I want to avoid conflict" or "I don't want to feel guilty.")
For both studies, 108 heterosexual dating couples were given a task to complete daily surveys for two weeks. This involved answering 26 questions about their motives whenever they had sex. The results:
On days when a person's motivation to have sex is more positively oriented, he or she felt more satisfied—both in the relationship and sexually—and had a higher level of desire. Conversely, on days when someone was motivated to have sex by more negative goals, he or she felt less satisfied and less desire.
It doesn't take genius to figure out which of the tactics boded badly for relationships. But seriously, if you're the type who prefers having sex just to avoid talking about serious relationship stuff, then it might be time to reevaluate your priorities.

[Wall Street Journal]