Why do we analyze the salt equation to find the pH?

[Protonated-Pam1D]

Can someone please re-explain conceptually why use the equation with the salt to find the pH of a solution?

[Wu Yuchen A1]

When titrating strong acid using strong base/strong base using strong acid, when equivalence point is reached, the solution is considered neutral.
When titrating weak acid / base however, when the equivalence point is reached, conjugate base/acid in the solution can react with water to form hydronium ion /hydroxyl ion. Then we have to consider the influence of such extra ions when counting pH for solution.