I didn't have space on my desk for a dual monitor setup (one day though) so I decided to go for one, really big monitor so that I could still have a large amount of screen real estate available when working with plug-ins and multiple windows.
I didn't need a 4K resolution monitor, as I don't do any graphic work or gaming, so this thing was perfect. Everything looks better on it, even crappy quality YouTube videos. Fits perfectly on a single desk with two studio monitors, a MIDI controller, audio interface, and peripherals.
Note: Waaaaay cheaper than Apple's displays. 5 stars.