Which pixel pitch is right for you is based on a combination of factors, which include:
1) The viewing distance, or range of distances, or your primary audience
2) The content you intend to play on the display (i.e. text only, or pictures or people or video or food, etc)
3) How big your sign is
4) Your budget

One size does not fit all. Even informed customers need guidance in this area to make sure the right sign is purchased for a given application.