Most computer displays these days are re-hashed TV lcd displays, hence the prevalent 1920x1080 pixel form-factor. This resolution limits the screen size on your desktop to maybe 24" - anything larger and your sitting too close to a fuzzy mess. I have two screens on my office computer - a 20" 1600x1200 (portrait) and a 37" 1920x1080. The latter is just a TV used via its DVI input, and is pretty awful to use for office apps like Word or Excel (but it's great for spinning around in the office and sharing when we're looking at application screenshots...). I suspect many people's expectation of a 'sensible' monitor size is actually based on what's available, constrained by this limitation.
TV's are obviously going Ultra HD (i.e. 3840x2160) - this will happen even though media content at this resolution will lag far behind. The price will be below $1000 in 2014. Ultra HD displays are just too good for digital displays for this opportunity to be missed. Even when viewing HD media content, at the very least you will be able to shrink the video window and display the online guide, or program info, or whatever on the same screen.
If you accept the above premise (Ultra HD TV's will become affordable quickly), the first benefit is to computer users who want a larger display. A 50" Ultra HD panel has excellent pixel density for a high quality display.
I can understand readers of this thinking "A 50" desktop display? That's crazy large and I'll never do it." but why at work in your office would you want a 80" desk and only a 20" screen?