The question isn't tricky at all, we humans are! The definition of sex is, the same, but people can perceive the same definition in various possible ways. For some it's a bodily pleasure, for a few it's an emotional attachment, for others, it also can be just a stress-relieving act. It depends on how a person views one's sex life. Sex always has something to with connection and all the people who carry that No-strings-attached tag also feels connected with the person they hook up with. Do you know that masturbation can make a person feel connected? Though it is a sexual practice in which one person is enough, he/she still feels the sensual, physical, and emotional connection. We all imagine, look at, think about someone while masturbating. Without a connection, we don't feel aroused, and we don't jerk off or finger ourselves. Sex and connection go hand in hand!
Sex does both, it promotes the connection and also can act as the placement of the connection as a strong substitute. The bitter truth is, it can do both the things for any couple but in different levels of a relationship. Do you think every day will be the same if you step into a relationship or get committed to a person? Hell, no! The constraint of love diminishes slowly, the aspect of responsibility elevates gradually, the trait of sexual attachments fluctuates regularly. So, don't expect your partner to be the same person throughout your relationship.