Since it’s enabled by default in OS X, many MacBook Pro owners with Retina displays take advantage of HiDPI mode - a setting that doubles interface element pixels on the x and y axis. Why should you consider a 4K display instead of a cheaper monitor with lesser resolution? It all boils down to clarity. If you own a MacBook Pro with Retina Display and desire extra screen real estate, then a 4K monitor can be a good investment, especially as the price of such monitors continue to dwindle.