If you’re unfamiliar with the term optimal viewing distance, essentially it means a distance from your television at which your eyes best observe the details offered by the resolution of your television. Each resolution (480, 720, and 1080) has its own optimal distance, but there can be other factors involved in how well you view detail, such as the quality of your eyesight.
A classic article on the subject is Carton Bale’s “1080p Does Matter – Here’s When (Screen Size vs. Viewing Distance vs. Resolution).” To help people understand optimal viewing distance, Bale created a chart (seen at the top of this article). Discussing the difference between 720p and 1080p at normal viewing distances, Bale reaches the conclusion:
If you are a videophile with a properly setup viewing room, you should definitely be able to notice the resolution enhancement that 1080p brings. However, if you are an average consumer with a plasma on the far wall of your family room, you are not likely to be sitting close enough to notice any advantage.
The 720p vs 1080p question is becoming a moot point, as production of 720p HDTVs has all but halted in favor of 1080p. But it may be interesting to know whether you are sitting too far away from your HDTV to take advantage of all that HDTV has to offer.