Marriage is a social arrangement, and these days, a couple enters into it less for relationship building and more to create a new set of attitudes and legal rights around their partnership.
Broadly, marriage is of benefit to society. A judging society (think in terms of both Extraverted Feeling and Extraverted Thinking here) likes for there to be absolutes. Example: a ring on the finger = someone has a life partner and must not be approached sexually, but may be approached conversationally without fear of such conversation being taken as a sexual advance. There's value in that sort of social certainty. The more things we can take for granted in any situation, the fewer resources we have to spend on examining and maintaining the situation. And that is quite possibly the least romantic thing I've ever written, especially as we're talking about marriage, but there you have it:
romance may be about possibility, but society
abhors it. Studies have shown that married people are more likely to do things that society (Fe would say "the Joneses," Te would say "the government") values: have children, pay taxes, participate in institutions, and abstain from violent and antisocial behavior. Consequently, society still confers certain benefits upon those who enter into marriage - the state of contractual matehood - and certain penalties upon those who exit it.
Now, many of the benefits and the penalties of marriage are nebulous, and their value and severity varies by region. A married couple in rural Mormon Utah != a married couple in progressive NYC, regardless of the fact that they're using the same bit of terminology to describe their union. A community property divorce in California != a divorce in a state like Ohio where everything is negotiable, even though both are called "divorces." It matters greatly who and where you are.
I am in my second marriage (I have been divorced). The benefits of marriage as opposed to unofficial domestic partnership - both of which I've experienced - are these:
* Financially: thousands per year in federal and state tax savings when married
* Financially: insurance (health, car, home, life, et. al.) and inheritance laws are more favorable to married people
* Socially: married women interact more, and more kindly, with other married women as opposed to single women***
* Socially: men (both married and single) are less hesitant in interacting with married women as opposed to single women***
* Socially: members of older generations no longer pressure you to marry (if that's an issue for you)
* Socially: religious pressure on your unmarried relationship, if any, is muted (there will still be pressure to have kids)
* Relationship: people feel and behave more relaxed in a marriage because marriage is theoretically permanent
* Relationship: people from a conservative background see marriage as proof of lifelong commitment, and many of them also see lack of marriage as lack of lifelong commitment
* Relationship: WRT children, children of a marriage are not stigmatized
*** Some people, especially conservative people who live in conservative places, do not draw a distinction between unmarried people who do have a partner, and unmarried people who don't. To them, single is just single. And if they have no way of quantifying the threat that a new or newly single person could potentially pose to their own pair bond, they will avoid the person completely. Yes, this is silly... we all know that a problem in my marriage is not the fault of a passer-by. However, certain second- and third-level effects of my marital problems can be avoided by avoiding unattached strangers. And this is the route that many conservative cultures take, to the detriment of singles and those who choose not to marry, especially women IME. Many people assume the unmarried are always on the lookout for a better situation. Marriage is usually the antidote to this brand of unearned social exclusion.
Again, the real tangible benefit of most of those things depends entirely on the area in which you live and the circles in which you move.
The problems of divorce are:
* Financial: assets are split. This may not be financially damaging in the long term, but it's always psychologically damaging. If we are married, and we have $500k, then you and I have $500k. If we divorce and split that, then you and I have $250k. Same amount of cash, but completely different degree of emotional safety.
* Social: social stigma exists for a divorced person, even if the informed world would agree that the divorced person was not at fault in the situation
* Social: some people reflexively withdraw from divorced people***
* Relationship: WRT children, children of a divorce are assumed to be worse off than children of married partners
* Also WRT children: divorced parents are often assumed to be self-centered... if they loved their kids more, they would have stayed married and "worked it out," etc.
Based on my own experience, I think marriage would offer the greatest benefit to a young couple living in a conservative area who did want children and whose incomes and asset bases were roughly equal. It would definitely pay off for them. The fewer of those descriptors were true, the less it would be likely to be of benefit. It would still benefit
society, but perhaps not the couple.
In my own marriage, the greatest benefits by far are social. G's an Extravert and I'm an INFJ. It's very important to both of us to fit in. For an INTJ it would be less so, although most potential partners are either Extraverted or Feeling (or both)... an INTJ might end up in a situation where, if you want a particular partner, you must marry because marriage is what's psychologically best for that person. And let's face it: most objections to marriage are ideological objections, not practical objections (all of which can be circumvented with judicious planning). Ideological combatants always end up wandering into the "do you want to be right, or do you want to be happy" forest. Some never emerge.
All that said, if (God forbid!) G were to die, I doubt I would remarry. I would want to emotionally, but protecting my children and my asset base from predators would be far more important to me than any of the intangibles I listed.