resolution - Is it better to edit photos with a high pixel per inch monitor?

Title says it all

Is it better to edit photos with a high pixel per inch (PPI) monitor or is a bigger monitor better?

eg. My current monitor

Panel Size: 23.6“ Wide Screen
True Resolution: 1920X1080
Pixel Pitch: 0.272mm
Brightness(Max): 300 cd/㎡
Contrast Ratio (Max.): 20000 :1 (ASCR)
Display Color: 16.7M
Viewing Angle (CR≧10)

So my PPI is 93.343 ppi

There are some monitors which are 21.5" and 1920x1080 giving 102.46 ppi

Or is this not really going to make a difference?

My D7000 can capture at a ridiculous resolution in comparison

Answer

This is kind of an ongoing debate, and it depends on what your goals are and how you edit your photos. I think that the naysayer argument, which I'll get into, can be considered kind of moot as you can compensate, and as such I am a strong believer in getting the highest density screen you can get your hands on. This debate as increasing merit as more and more photographic editing tools are finding their way onto tablet and phone devices, which have pixel densities well over 150ppi, with some phones pushing 400ppi these days.

Lower (but not low) Density Argument

The argument for using a lower (but not necessarily low) density screen usually comes from pixel peepers. The general argument is that as screen PPI increases, your ability to evaluate detail at a "pixel" level decreases. There are pros and cons to this argument, ironically giving us a slight recursive problem. In general, it is easier to "pixel peep" with a screen that is 72ppi than one that is 103ppi...the pixels are simply larger, and the pixel spacing can improve contrast a bit. There are caveats to this, however.

First and foremost is the debate about whether pixel peeping is really beneficial in any respect when it comes to photographic post processing, or if it just brings to light problems that, in the vast majority of presentation formats, are completely irrelevant? Pixel peeping can bring to the surface extremely minor issues, such as the slight softness of high density camera sensors (i.e. 18-24mp APS-C DSLR sensors), a slight amount of blurring due to camera shake that does not generally matter, very slight focus error issues, etc. I won't get deeply into the pixel peeping debate, but I think high PPI screens fall into the same bucket...it's generally a moot point. You can frett about it, or think of it simply as a tool, and nothing more.

Second is the notion that with a higher density screen, you could not pixel peep as well. With a very high density screen, such as an Apple Retina display (~360ppi on iPhone, ~250ppi on iPad) pixels are small enough that you really can't see them from a comfortable viewing distance (which is the entire point). Some Android devices have pixel densities even higher, making any per-pixel work pretty much impossible. Well, assuming you actually want to do per-"screen pixel" work...there are ways around the problem.

Finally, one of the arguments against higher density screens is that more pixel processing requires more horsepower to do the processing. This is true, however that has more to do with screen pixel dimensions rather than screen pixel density. You mentioned both screens are 1920x1080, so despite the fact that it is higher density, the alternative screen won't actually incur a performance hit...you'll still be processing the same number of pixels.

High Density Argument

The argument for high density screens usually comes from avid pixel-peeper-haters, those who naturally don't concern themselves with minute issues like slight camera shake or slight focus error, and those who have a deeper understanding of the technological and practical benefits of a higher density screen.

With high density screens, you usually have more screen space to work with (on desktop ready screens). This is a huge benefit when you want to fit your whole photo on screen without having to reduce it to an unusable size. I personally use the Apple CinemaDisplay 30", which sports a little over a 103ppi density. (Better screens for photographic work include the similarly-sized Eizo and NEC 2560x1440 LED screens, which offer far better gamut, better color correction, and better white neutrality and brightness across their screen area, at a 109ppi density. If you are looking for the highest density screens with the best photographic-editing quality available, look no further than these screens.)

The large screen area combined with a small pixel pitch is superb for photographic work. Most output formats, either for the web (which are 97% of the time very small downsized versions of the original RAW image) or for print (which tend to have higher pixel densities ranging from 300ppi to 720ppi) will diminish and absorb those small defects caused by high resolution sensors, slight camera shake or slight missfocus.

There are good cases to make for having the highest PPI screen you can get your hands on, even at 250ppi, 300ppi, 360ppi (tablet and phone level). All three of those pixel densities are similar to common print densities, such as 240ppi, 300ppi, and 360ppi. Being able to accurately preview a properly prepared (exposure tuned, scaled, sharpened) photo for print at one of those resolutions (or double, such as 600ppi/720ppi) is almost a holy grail for photographers who print their own work.

One of the key arguments of high-ppi naysayers is that you can't pixel-peep with a high density screen. In one sense, no, you can't pixel peep if that means RAW image pixels are the same size as screen pixels. However, there is no mandate that says one must only pixel-peep at screen-pixel size. Tools like Lightroom or Photoshop offer the ability to zoom into a photo well beyond 100% (1:1) zoom. If you have a high DPI screen the simple solution for pixel peeping the photo is simply zoom accordingly. Using a 300ppi tablet...zoom 3x, or 4x. Your photo pixels will not only be about the size of a 100ppi or 72ppi screen, but they will be far clearer and with better contrast than when viewing them 1:1 on an actual 100ppi screen. You should have the option of zooming 6x, maybe even higher...if you really want to pixel peep. For photographers who print large, wherein preparing an image for print requires enlargement by 2x or even 3x, high-density proponents make the argument that a high density screen improves the ability to soft-proof and preview IQ at print-size without actual physical screen pixels getting in the way.

Personally, I say go with the highest DPI you can. You can always zoom in more if you want to pixel peep RAW image pixels. The higher density will make the aspects of the hardware less intrusive, smaller pixels closer together improve the contrast of image detail (as screen pixels can become sub-image detail level, etc. Other things become a lot better with a higher PPI screen as well...such as text and UI elements. Edges are sharper and higher contrast as well. I'd say go for the 103ppi screen...you can't really go wrong, and the benefits are so many.