Sex is a skill.
Practicing a skill = being better at the skill, more open to other possibilities (on average), and being better with your partner. Some things one learns predominantly through partners who have been involved in such before or one only realizes are possible with a partner who has a particular skill set.
Finally, it helps when your partner is sexually frustrated and does not know why (or you are, for that matter). Experience helps with diagnosing the problem and ascertaining the solution (which can range to lubricant or needing more/less foreplay to needing to be dominated or needing to dominate, it varies by the person).
Simply put, it is fun. I believe that if you do settle for one person, who want to bring a good skill set to the table that you can hone to that particular individual. Tempered steel and all of that.
This is not to say that one should rush into it, but I also don't believe postponing simply for the sake of postponing it is the answer.
Sweeter to wait? Maybe for some, others would find it "sexually frustrating." In my experience, it also makes one more willing to rush the relationship itself. I've seen more than one couple get married basically as an excuse to have sex within the framework of their beliefs (although they wouldn't have named it such). They are basically still in the
limerence stage and have very strong sexual urges (we are sexual creatures, after all), so they rush through the early stages of the relationship.
This isn't getting into the broad number of people who do not date with the intention of getting married. They play relationships a day or week at a time, and if it turns into a marriage so much the better, but that's not the end goal of the dating process for them.
Basically, my theory is that one should postpone until you are "ready" and comfortable with yourself. My rule is that even if the relationship were to end tomorrow you wouldn't regret the action that night. After that then treat it how you want to treat it. If you need to wait for marriage, there is nothing wrong with that. There is nothing wrong with postponing with a partner 9 months or five years if that is what you both want. By the same token, just as one should have sex for what are the "right reasons," one should
not have sex for what are the right reasons as well.