I have no idea how to answer this question, since the answer is so culturally specific. It didn't really come up with Sam and I started dating because, frankly, neither of us had anything else serious going on at the time. We seemed to consider ourselves An Item pretty early on.

I think the short-term-serial-monogamy situation davetheinverted mentioned has been the norm for high-school and college students since at least the 1980s. It was confusing when I was a kid, because layered over that many people still had this ghostly vision of 1940s-1960s dating norms, in which you were supposed to date lots of people nonexclusively and "going steady" was a big serious step, that didn't really apply any more--and when you get a date for an event, like a dance or a wedding, that older idea of nonexclusive dating might still apply to some extent.

I think something like it also applies to older, adult singles actively looking for long-term partners, especially if they use dating services; they may go on lots of dates that are treated almost like a job interview process. I never really did this and it sounds profoundly dreary to me, but it seems to be common among post-30 unhitched professionals in large cities. As for when you're exclusively hitched, I think that is probably going to depend enormously on the local culture; there are people for whom sexual skill/compatibility is extremely important who may well treat sexual intercourse as just another part of the trial process, and there are other people who won't.