For me, the No. 1 reason to get married is that, because I'd committed to one person, I wanted to make sure that if anything happened to him, I would be able to take care of him. For instance, if it comes down to life-or-death medical decisions, I know I will do my best for my husband, and vice versa. If anything happens, it will be decided by me or him, no one else.
If I'm commited to one person, I will not let anything keep me from taking care of him, including all the benefits that go to spouses in case of injury, death, etc., such as Social Security, pensions, insurance, other inheritance rights.
Of course nothing is certain, people change and can grow apart, and divorce can be messy and expensive. That's what marriage means to me: that I'm willing to take those risks because that's how much I believe in my husband.