Man on top is the most popular sexual position for lovemaking. It's sexy, it's comfortable, and it allows the man to feel dominant and the woman to feel feminine and receptive to her man – perhaps even to feel a little like she's being "taken". Many women say that man on top sex makes them feel safe and protected. It's certainly a good position for intimate kissing, bodily contact, and looking deeply into your partner's eyes as you make love. Besides all this, it's a very easy and natural way to make love. In fact, man on top is a sex position which is ideal for almost everyone: It's the most straightforward and possibly the most satisfying position of them all. And there are many ways to enjoy it.
I guess I am starting from the assumption that sex in most positions is a great thing. What's unique about man on top? I agree that it is a really comfortable position, especially for women: we can do the lazy, proverbial "lying on our backs" thing and enjoy. It is a very intimate position from a woman's perspective and very relational. The partners can see into each other's faces and eyes, which can be loving and alleviate insecurities for both partners. The man on top position is probably where most people start out with each other. It's safe and culturally acceptable and reaffirms gender roles for males and females.
What are the drawbacks of the man on top? Actually, I think there are quite a few. Firstly, it restricts women's pelvic movements and means the female partner has to be fairly passive. It's really hard work having to lift your pelvis off the bed and thrust against gravity and your man. This translates into you guys having to do all the physical work during sex, which can be exhausting and a real turn-off. What if you want to have sex, but you're tired from your day at work? (Answer: don't choose this position). Your body might be more inclined to give up on its erection if you are tired and you are having to be quite active as compared to a position in which you need less strength. After all, man on top means you thrust, and it also means you need to support your body weight off the bed for a prolonged period of time.
Also, man on top doesn't allow the woman to adjust the angle of her pelvis much, so she can't direct his thrusts easily to the areas inside her vagina where she can feel him best. However, sex in this position can feel safer for a women due to her internal anatomy: her lover will thrust towards the bottom and back of her vagina and there is less likelihood of his thrusts touching sensitive areas inside of her body such as the G-spot or the cervix, the latter possibly being quite uncomfortable if she is not psychically aroused. Of course, if you are into relaxing and chilling out during sex, man on top is great (if you are female, that is).
Another major consideration for the man on top position is that sustaining eye contact right through can feel claustrophobic during sex. You may feel like all your reactions are being watched or that you have to be constantly emotionally available to your partner rather than being able to give in to your own physical sensations. If you're struggling to stay with your own sense of arousal, eye contact can be very distracting. Also, it's easy to notice distraction or insecurity in your partner's face, which may only be there temporarily, but which starts to ricochet between both of you and ends sex all together.