Some holdings in a portfolio are weird basically because they are not there just to make money; and that does, indeed, seem odd. Why else would someone hold an investment other than to make money?
The answer is because, as any economist will tell you, not losing money is the same as making money. If I avoid the loss of £X, then I am £X better off than I would have been, all else being equal. In effect, therefore, I have gained £X.
And this is more than a contrivance. In a portfolio of securities, where values are rising and falling roughly in a uniform, though unpredictable, fashion, it is good to add some assets whose values tend to move independently of the others; to rise when the others fall, or just to remain stable. It preserves value; in effect adding value when otherwise there would have been a drop. Of course, like any benefit, it comes with a cost. Independent movement can mean some values fall when the group as a whole rises, thus reducing the gains that would have been.