>>11499168
Like any thing or process, priming can be helpful or unhelpful depending on the circumstances, there is no one size fits all rule.

You might want to prime when
>you have resin and/or metal
>the surface has defects that need one or more rounds of fixing (including defects you created yourself while seam welding etc)
>you want to simulate shadows in recesses and hard to reach areas
>you are using non-lacquer paint

You might want to skip priming when
>the surface has intricate detail that primer can fill in
>the surface is already perfect and you plan to paint shiny metallics like chrome
>the surface is the right color that you want to use as is to match the part you can't paint (e.g. skin tone to match the face plate with pre-applied eyes)