Some would say hyphens are going the way of dinosaurs, disappearing in favor of compound words. But they are not extinct just yet, so knowing when to use one and when to skip it is important.
The difference between “high-quality” and “high quality” is determined by the location of the noun that the phrase should modify. High-quality indicates a compound adjective where the word “high” modifies the word quality rather than the noun that follows. The only time you don’t need a hyphen is when a noun does not follow the phrase.
Sometimes, removing the hyphen can cause confusion for readers in understanding what a compound word or phrase is modifying.