They flower and they quickly lose the leafy bit that we eat. The flowers are handsome, and you can save the seed eventually, but they take up space, of course.
I have heeled leeks in and found they went soft and peculiar. But that's only my experience.
I think I would freeze them in very concentrated leek soups and so on that I could add potatoes to when thawed. Or leeks in cheese sauce, or whatever it is that you like eating. Or fry chunks gently in a little butter for a few minutes, quickly cool and freeze, and carry on cooking them later when thawed?