Tough question...that depends on the level of commitment and the type of sex. Recreational sex requires no personal relationship.

Depends on my objective at whatever phase of life I'm in ...

I personally can't have sex without becoming attached. So, it may start out in a casual way, but if it continues for any length of time, and I want it to continue, I begin to become attached. I suppose this is due to brain chemistry, which increases greatly during times of intimacy. Once this happens, I believe my brain is changed in some way, either by forging new connections, or by becoming addicted to the chemicals. I don't know. I am undergoing such a relationship at the moment; it is dangerous for my well being, due to certain circumstances, and I don't know how to stop it. :'( Christians might say "turn it over to God", but an agnostic like me has to live with this attachment in every cell in my brain, and it's very tough.

I won't enjoy sex unless I can trust my partner. Trust doesn't just happen, it has to be built.

I have to at least like the person I am having sex with...as a sapiosexual, it is hard to enjoy sex without at an intellectual connection.

I am going to choose very important because without a close personal relationship, sex would not be happening...it does not mean that I am committed except when I am with my partner.

Varies with the individual

I think how important it is, is the individual's call.

Some can experience great sex with people they're not emotionally attached to, or with whom they don't feel a strong mental connection.

For others, like me, one may need to really like and or care for someone, to have sex.

Some have called me a prude, but they miss the importance of really trusting the person who's doing you upsidedown while hanging from a zipline.

In a general sense, relationship is not a prerequisite for sex. However, for certain individuals, it very much IS. If the question was directed toward me, personally, a close relationship is needed before I consider getting physical. Conversely, physical attraction is needed up front for me to feel romantic toward someone.

Sex can be anything from a moment of shared pleasure between two people who want nothing more from each other to an expression of love between two people who have been exclusively together for a long period of time.

So long as both parties are honest with themselves and each other regarding what they want from the relationship, it’s a personal choice which shouldn’t be mandated by any government or religious organization beyond punishment for the use of coercion or harrassment to gain sexual Congress with another.

There is "sex"...And then there is "sex in a relationship."

Nothing beats sex with someone you love and trust. I believe they call that making love!