Truss used more application. In general, trusses used to roof structure or bridge structure. you can analyze trusses by many method such as joint methods in first picture or Finite Element analysis method in second picture.
Nowaday, Using program to design truss such as Finite element analysis for convenience and quickly analysis. That design of common structure are equal cross section area to make and created easily. But it is over design. Because some element have little load should not big size. So that use Optimization with Finite element analysis to design.