I should pre-empt this with, I am in no way judging anyone by writing this. You may do with your genitals what you like, as I do.
I have had sex with 4 people. They know who they are, or I at least hope they do or that could be embarrassing. Two of those people were long term boyfriends, one of them was the exception that proves the rule and the other a blip. I have not always had this rule, I have explained in detail that has harrowed both me and you when such a time I completely broke this rule. I first said the words 'I don't do one night stands' to myself in a mirror, like I was in a bad student film production of Cabaret, the night after one almost one night stand. I have had not had one since.
I should clarify that I don't mean that I am in any way prude. I just don't think I am equipped with the social skills or emotional strength to have sex with someone I don't know and then never again. I tend to fall apart and become one of those girls you hate when I first like someone so if they held my hand and then never again I could become distraught. Also when I say I'd prefer to 'wait' to have sex, I'm not talking in a bad 90's american teen drama way, I mean like a couple of weeks or a few dates where you can decide between both parties that this is probably going to to further and that it is likely you will sleep together more than once. It doesn't have to be openly discussed but I have found that it doesn't have to be because the more you know someone's likes and dislikes, if they have any pets and which celebrities they hate; you are much less likely to want to 'love them and leave them' so to speak.
The more emotionally attached you become to someone and the more you see them as a human with beliefs, feelings and tastes you are more likely to make an informed decision on whether or not you want to sleep with the person in question. I once read an article that said if you are confronted with someone pointing a gun at you that you should tell them the names and ages of your immediate family and your favourite television show. Its 90% less likely that someone is going to shoot you in the face if they know those things about you.
Yes in this analogy I am likening one night stands to being shot in the face. I still have no judgement its just the only example I had to hand.
When people ask me why I don't do one night stands, which they always do, I joke and say 'I'm too good in bed, they need to work for it' and although I am far too good in bed to waste it on someone who may have made a maximum of a few hours of effort I also believe that sex in general is too good. Its too good, fun, personal, intimate, brilliant and tactile to be wastes on people who aren't worth you. But next time someone asks me, I'll just show them this. Its more accurate.