What are vertices (vertex shaders) on mobile?

What are vertices and how to reduce them for optimal performance?
(Is the stats window in game mode useful to indicate performance on also mobile?)

Unity uses two different method for calculating the lighting effect of light sources:

  1. Vertex Lighting : faster calculations, lower quality, supported by older devices and phones
  2. Pixel Lighting: slower (lots of calculations), higher quality, supported only by new phones. Light cookies, normal mapping and realtime lighting can only be performed by pixel lighting method.

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More information here.