Example: My first husband gave up a pretty good job to move across the country, where he had to start at the bottom in the credit department of a large retailer, to support me while I was in law school, earning nothing for three years. When we divorced, several years later, I was making a better income with a better pension plan than he had. I agreed he could have the equity in our house in exchange for no alimony and our both keeping our respective pensions. We both came out OK. But if he hadn't agreed, he would have had a pretty good claim for alimony, based on his giving up income, supporting my career, and my increased income prospects.
And I think it would have been fair, had we not arrived at an alternative agreement that recognized those sacrifices and contribution.