If any aspect of a pic intrigues me, I save it for reference. I then hope one day that I will find it in higher quality to enjoy it more.
And, it can be anything. A color combination, a weird perspective, an interesting idea, an unusual artistic take on a classic theme, a well-composed expression on one person's face. Even, a picture that is deeply flawed or outright bad, if it is a good example of something that was done wrong and can provide insight into how I might avoid that mistake.
And, also, this: >>7667268
Sometimes a composition just works as a pape, even if it's imperfect. It just makes a good background. Different moods for different days.