if you intend to use it as a monitor for the best picture quality.
B1) What is Chroma Subsampling?
Wikipedia explains chroma subsampling very well, so I’ll defer you to there: link.
In summary… Chroma subsampling is a process where color information (a.k.a., chrominance or chroma) is sacrificed in order to reduce bandwidth. Why sacrifice color information? It’s because of the limitations of our eyes. The human eye has poor color acuity for detecting color details -- especially on a moving object.
Chroma subsampling sounds like an awful idea, but think it in terms of individual pixels (which is the level where subsampling works its magic). Let’s say you have a column of bright-red pixels and another adjacent column of dark-red pixels. With subsampling, you’ll end up with two columns of bright-red pixels instead. Unless you sit 1 cm away from your TV and have the eyes of a hawk, it’s highly unlikely you can detect the difference. Compound the fact that typical video footage is a series of different images being displayed at a rate of 24/30/60 fps, subsampling becomes imperceptible to the human eye.
B2) What does “4:4:4” (or 4:2:2 or 4:2:0, etc) mean?
Again, Wikipedia explains this very well with illustrative examples: link. For more technical descriptions, check out these pages: link1, link2, link3.
For you audio-visual learners, this youtube video explains the nomenclature very well too: link.
To sum it up, 4:4:4 means no subsampling is used at all -- so your image is displayed in its purest form. Anything less than 4:4:4 means original color information is lost.