The phrase "why buy the cow when the milk is free" is a proverb used to suggest that it is often considered unnecessary to make a costly commitment or investment if one can already obtain the benefits for free or easily. It serves as a caution against overcommitting when immediate benefits are accessible without obligation. Historically and culturally, this saying has been used especially in the context of relationships and marriage. The implication is that if someone is already receiving the benefits (like companionship or sexual relations) without formal commitment (such as marriage), they may be less inclined to make that commitment. In essence, the metaphor compares buying a cow (making a commitment) to obtain milk (the benefits), and questions why one would purchase the cow if they can get the milk without it. However, it also highlights the value of commitment and the deeper rewards that may come with it, beyond just the immediate benefits. The phrase can be controversial or viewed as outdated, as it reduces complex human relationships to a transactional analogy and has been criticized for being dehumanizing or oversimplifying. To summarize:

• It's used to question why someone would commit or pay for something when they can get the benefits free or easily.
• Commonly applied to relationships to comment on the idea of marriage and sex.
• Reflects a cautious view on commitment, emphasizing convenience but also warning about the value of true commitment.
• Has cultural and economic interpretations about weighing costs and benefits before investing in something.

This expression is often understood as a cautionary saying encouraging people to consider the value of commitment and whether it is necessary when immediate benefits are already being enjoyed.