if not, would you ever consider it?
Sounds like I am gonna write a longer comment to reply to this, why not making it a post.
I did move permanently to another country twice (first time when I was a child, wasn't really my choice). The other time was for work.
Moving to another country is a lot of stress.
We often think of ourselves as self-contained individuals, like... if you move yourself to another planet, you may be lonely and maybe you won't gain new skills, but you'll be *yourself*, and you'll preserve all the skills, knowledge, values, and so on, because they're in you. You'll live happily (with a reservation of extra loneliness) given you have everything you need, food, entertainment - maybe books, etc.
Moving to another country will make you understand that human being have a lot of their identity in their environment. Tools they use, habits they have, their friends, their job and their workplace, town they live in, and so on. Change all of it, and suddenly you're only 30% of what you were before. It's a tremendous feeling of loss. Also, big part of your knowledge is suddenly not applicable, obsolete - it's like you never knew it. It takes years to rebuild missing parts of identity, "find yourself" again in the new environment.
Back to more down-to-earth analysis.
1. Huge stress caused by identity crisis. Feeling lost and disoriented. Time and effort (energy) to recover. Probably some 2-5 years (I think was 4 years for me). It slowly goes downhill, then reaches its peak, and then goes uphill relatively quickly.
2. Often delay in career. For some people significant downshift. Your mileage may vary, but it may last anywhere from 1 year to 6 years (on the longer side if you need to learn language and get a new higher education).
3. Extra stress caused to adjusting to new environment, learning new household tricks, finding out all essentials. Just legal paperwork (driving license, credit history, bank accounts) can easily add several hours a week to the entire first year. Think of moving from one state to another, but multiply by 2 (only for p.3, but for p.1 you may multiply by 10...)
1. After several years, when you recover, you gain deeper insights about all aspects of life and multi-cultural perspective, that can be advantageous both in relationships and in further career.
2. An opportunity to rethink yourself, your values, your direction in life, create better habits. If life was in stagnation before the move, then the move can be a significant boost of new perspectives.
3. Wider network. If you maintain connections with old friends and make new ones, here you go. Net benefit.
4. New language. Langauges develop brain in various ways. Extra points if you preserve your old languages (keep them afloat by speaking with your old friends, writing, etc).
5. First year, especially first 3-6 months, everything is new. Brain is actively processing a lot of information. You start seeing things that you didn't see before, because you were so accustomed to them. Talking about purely visual aspect. Like... trees. You see the same tree every day, and the brain learns to totally ignore it. You see just a tiny bit of it, and the rest of the picture comes from memory. After the move, everything is new: you see it all. This can give boost of energy, and may help to cope with drawbacks.
Depending on your health, on your luck, on your goals in life, on how different the other country is, this may end up being positive or negative. I know people whose life was totally ruined after permament move (they moved after 40 y.o. and it was their first serious move, out of necessity), I know more people whose life became better but over time. I think age is also important: the older you move, the harder it is, and with years until you see benefits, you may lose necessary health to be able to enjoy them.
Moving for marriage? It depends, but I guess, on average, it's bad idea, unless you already lived together, and/or you have other reasons to move and marriage is only one of them.
The worst case I can imagine is put all negative factors together:
1. You're 30+.
2. You never moved to another country, and you only know one language.
3. You have very specific career, that doesn't exist in another country - you'll need to get education again.
4. You never lived with the person you're marrying.
5. You're going to move as dependant.
6. (If you're a woman) he wants family and children (so you'll get all the stress plus a housewife's fate for years, until you get a chance to get a new education and job).
7. He isn't rich, so you won't be able to see your old friends and family often (travel is expensive).
8. A new country is significantly different in culture from the country you're moving from.
9. The climate is different (consider new illnesses, allergies etc).
Now everything will change: friends, family/person you live with, job, place/environment and language, and some aggravating factors on top of this (age, lack of experience learning new language, etc) - that's maximum risk.
If you can minimize numer of things you're changing, it can all go smoother.
RE "mail-order" brides (you date a girl from another country and bring her in to marry): I've heard plenty of real life stories of fail, and very few success sories. Too much change is risky for both sides, and dependants are expensive for the inviting side.