I have had sex on the first date maybe 3 times (a few hook ups, but those I wouldn’t consider “dates”). Anyways one of them it most definitely ruined the relationship chances. I dunno why but no relationship ever came of it despite a big mutual interest. The second one and I weren’t really a BIG dating opportunity (we had our differences), and despite some efforts by myself we never went on another date.
The third, final, and most important of them, ended up being my g/f for 8–9 months. We managed to get a working relationship out of it for a while. But i’d be lying if I said I didn’t think it had a detrimental effect on our relationship. I don’t think we ever “fully” established an emotional connection like we would have had we put off the sex. It was not the reason we broke up though.