ShowSynthesisResult[linkage] displays the result of the synthesis in plot. The plot shows the accessible joint range of the driving variable and the the crank angles of the synthesis.
The synthesis result plot could be used for checking the "drive-ability condition" of the synthesized linkage. Depending on the type of the synthesized linkage, there might be a solution of the 3 precision point synthesis, that could not be reached by continuous movement, because the feasible range of the crank angle does not permit it.
Synthesis result that could not continuously driven: