Sex is a fundamental part of our genetics as it is for procreation. However, if you are not interested in children, sex is still a very important part of relationships.
I have never had casual sex, however I feel that sex with my partner is an important part of our relationship due to the extra intimacy it provides us. I feel sex is very much worth it.
However, as another hubber wrote, it is entirely your personal choice and you should never feel pressurised one way or another.
I hope that our comments have helped in some way though!