Well I think the point is not that you never get anything out of it or that you should always be sacrificing yourself, etc.

But an important aspect of relationships is transformation and personal growth. There are moments in relationships where you would be saying "I should do this for the sake of X". And the "X" could be based on your personal or relational values. Making decisions based on that would mean that you're not just "getting something out of" the other person or thinking "What am I going to get in return if I do this?". Do you benefit from it? Yes, possibly, but you're not exactly expecting anything from the other person.

Basically I think thinking of relationships in terms of "transactions" is to bypass having to have those values.