Getting married to someone means you say "I do" to your spouse and promise to be with them through sickness and in health, through thick and thin. But, when you marry someone, you don't only marry your spouse, but you also marry into their family.
You not only gain a husband or a wife, but you gain in-laws. And, for some people, gaining in-laws means you are gaining new, life-long friends and family to spend the holidays with, and all the in-betweens, too.