Given an original formula $\varphi$.
The equisatisfiable formula in CNF after Tseitin encoding -- $CNF(\varphi)$ -- is \emph{linear} in the size of $\varphi$, since the number of variables and clauses introduced by Tseitin encoding is \emph{linear} in the size of $\varphi$. 
Using a truth table could result in an exponential blowup when constructing a CNF.