The higher the screen resolution the greater the memory and processor requirements are for displaying everything at full resolution. But generally with enough processing power and memory there usually isn't too much of an issue with performance. Just to put that it into perspective, I've used a machine with a 2.7GHz core 2 duo processor with 12GB of DDR3 RAM, and an FX2700 with 512MB of dedicated VRAM at 1920x1200 resolution running on an Agility 3 SSD. Even this setup struggles with 2D rendering within the Windows environment using none Aero classic visuals when using certain applications for audio.

With a 17 inch monitor, setting it at 1920x1200 resolution definitely improves the visual quality and details of the viewing area on screen. The screen is generally large enough to notice a huge drop into fuzziness when setting it to any resolution lower then 1920x1200. So the number of pixels per inch whilst set to 1920x1200 resolution is just right for the monitor size. Its perceivable to the point where you will notice the difference in sharpness and clarity at full resolution. A monitor of this size could probably benefit from an even higher resolution for improving picture sharpness and clarity that’s noticeable to the human eye, but it will obviously potentially slow down the machine even more so on the same hardware specifications and current software/system driver implementation.

The human eye is said to be able to perceive 300PPI (pixels per inch) , but surely its also relative to the physical viewable size of the screen too?

For example would there be any point having 1920x1200 resolution on a,4, 5, 7 or 10 inch screen if the extra resolution isn't actually noticeable? As it would pretty much need extra processing  power and more RAM to handle it which would either slow it down if you have a slow processor, or possibly require more electrical power for faster processing thus causing shorter battery life on portable computing devices such as smartphone's and tablets. It just seems like a waste of processing power and memory resources. Case in point, there were apparently a bunch of tablets by various manufacturers with 4K (4,096 × 2,304 resolution) displays at CES 2013, and generally most of them were said to be very slow when using them.