Labels are useful as more than just a tool for the marketing department. Labels also help the consumer determine if the product before him is the sort of thing he wants to purchase or not. Still, labels can be limiting, deterring someone from acquiring something worthwhile merely because it doesn’t precisely fit within a genre box.
Those of us who are aficionados of Sword-and-Sorcery fiction expend significant time debating what is or is not S&S. That’s as it should be: If your goal is to consume, enjoy, and discuss X, you want to avoid slipping in discussion of Y as beyond the scope. But S&S is a protean subgenre, a slippery subject that is, at the same time, gregarious and outgoing, liking to socialize with all the neighbors in the bookstore. So you can’t always be sure if the book next to that copy of Swords and Ice Magic is S&S or instead Sword-and-Planet, High Fantasy, Grimdark, or something else entirely. And whether or not it matters is completely subjective.