What is the origin of the idiom "la-la land" and when to use it?

The idiom "la-la land" likely originated from the phrase "la-la" or "la-la-la," which is often used to represent a nonsensical or dreamy humming or singing sound. This expression refers to a state of dreaminess, unreality, or being out of touch with reality. It is primarily used to describe a state of being out of touch with reality, typically when someone is lost in their own world, daydreaming, or not facing the practical aspects of life. It can also be used to criticize someone for having unrealistic or impractical ideas.