(after snorkling coffee everywhere from reading the other answers
)
ASSuming you are:
1. A US citizen;
2. Going to sponsor your intended spouse;
3. Your intended spouse intends to live in the US with you;
The biggest issue you should be aware of is the legally binding I-864 Affidavit Of Support.
This is part of the package you would submit in order to obtain residency for your spouse. It is, essentially, a promise to the government that your spouse will not draw welfare (federal funds such as food stamps and TANF); in the event of your divorce you would be responsible for not only reimbursing the government should your spouse obtain this help, but also for ensuring your spouse is supported to the amount of 125% of the federal poverty guidelines (about $1000/month give or take).
Your obligation remains until one of these conditions is met:
Your spouse earns enough qualifying SS quarters (works for about 10 years);
Becomes a naturalized citizen;
Leaves the country permanently;
Dies.
Best case scenario:
You marry spouse. Spouse naturalizes and becomes a US citizen. You then divorce. Your obligation to support your spouse has ended.
Worst case scenario:
You marry spouse. You divorce spouse before any of the above conditions are met. Spouse uses I-864 to sue you for support. You're now on the hook for $1000/month (or at the very least, if your spouse works it will be the difference between his/her earnings and that amount).
Of course you could be wanting to live in your spouse's country, and/or your spouse could have already earned enough SS quarters to make the whole thing moot.
But there you have it.
It IS something EVERY potential sponsor needs to consider very, very carefully.