I'm not averse to withdrawing and ejaculating outside of the vagina at all and its always been one of very many permutations in our lovemaking.
However for those in pursuit of mutual orgasms, especially early in sexual relationships it can be counter productive. We're surely aware that women do tend (generalising) to be slower to achieve a climax, hence the problem of premature ejaculation. Here, by premature ejaculation I merely mean that the man climaxes before the woman.
It's certainly a trigger for a woman's climax when she feels the spasms of her partner and hopefully the force of the ejaculate inside her vagina - we talk of the ejaculate 'hitting' the cervix - and is very likely to be just that which brings about that much sought mutuality.
When the relationship is on a surer footing though it is often the desire of women to witness the ejaculation or even to feel the ejaculate externally 'bathing' their vulva. It can be a manifestation to them of their partners virility and manhood. And it opens the door to other activities such as 'tongue cleaning' of the womans body, tasting from the fingers etc.
One thing though I personally dislike, is the image of the man towering over the woman masturbating onto her, a la bukkake. It smacks to me of subjugation though here again if its mutually desired then thats fine.
Like many I love to be taken to climax orally and in many cases the mutual orgasm does not obviously feature, except that is when positions such as 69 are used.
There comes a time when such variations keep alive the intimacy of a relationship but in my view, early in a relationship, what I describe in para's 1 and 2 is important to establish first.