If you can handle it, knowing as much as possible is best. Information about a potential mate is crucial in understanding who they are, and how your relationship most likely will progress with the person.
Dont be naive, and just say "the past is in the past" and ignore anything she has done up to the point you met her. A person's past makes who they are, so you better pay attention to it.
I can completely understand if a guy doesn't want to know about a girls sexual past, if it works for them then they can go ahead with it. But from my experiences so far, a girls sexual past has effects on your relationship. Consider things like traumatic experiences, they cause barriers between the two of you if they are unresolved; a very high partner count can significantly reduce the effects of pair bonding; and a history of nothing but short term flings indicate a tendency to avoid long term commitment.
One more thing, don't just wait until the red flags are blatantly screaming right in front of your face. At that point you will be too attached to leave so easily. Be on the lookout from the beginning so you can spot them sooner. This way, you will save a ton of time, money, and heartache from being with a woman who ultimately was never good for you to begin with.
