This was 100% banned at our table...
... 30 years ago. We were young and immature then, and it lead to immature and creepy play when boys played women. So we said "erm, no", and I formed he opinion that cross-play was a bad idea, period.
As a result, I rarely have crossplayed. But looking back now, I see that if you have players with a certain level of maturity, it's not a problem at all - it's only a bad idea with immature, horny/creepy players.
It's interesting that this came up today, as I will very soon be playing a female character for a few sessions - my regular character is out of action, and for background reasons the replacement is a woman.