While I realize the question was directed at single straight guys and I can only check one of those boxes, but since swinging was kind of like dating to me, I can lament about missed opportunities about not taking photos of some of the women I've fucked, whose faces and bodies only exist now in a fading memory.
Only once was the topic every brought up by a couple who asked about taking pictures of our foursome exploits, but neither my wife nor I were keen on the idea at the time, having just met them. Though we eventually become pretty close with them and swapped regularly enough to trust them, they never brought it up again and I forgot about it much to my regret after we stopped seeing them, as I would have loved to have had some pictures of the other woman so I could jerk off to and remember how enjoyable her body was. But alas...
No other couple we were ever with brought up the topic and I would have felt uncomfortable to suggest it. I guess for someone to allow others to take naked photos of them it all came down to trust. Trust that the other person possessing them would not show or post them anywhere else, which would be even more risky if the pics included faces and thus whoever was in the pics had no control over editing them or hiding identifying features. Also, a lot of the places I was with these women were clubs or house parties where there are strict rules against taking pictures or videos. So, while having naked photos of them would have nice, but I would have even settled for just a G-rated face or clothed body pics to remember them by.
So, to date, the only photos I have of a woman I've fucked has been my wife, whom I've been taking shots of since the earliest years of our marriage when an instant Polaroid photo was pretty much the only option to take nude snaps. Over the years I've occasionally used some of those older pictures to masturbate when the opportunity arose, because despite the fact I can still fuck her whenever I feel like it, I found I also enjoyed using those photos to reminisce about her back in her younger days when I was still discovering things about her, her body and her sexuality. Since then, I've of course shared some of those pics online (both here and elsewhere) and even though those viewing them have more than likely not ever had the opportunity to fuck her, but I like thinking that some guys seeing them might be wanting to or even jerking off with them.