Why does each chemical reaction have many possible balanced equations? of all possible balanced equations, which is preferred?

Each chemical reaction, you may say that there are many possible balanced reactions since the coefficients of the reactants and of the products can be another set of numbers as long as the ratios of the compounds would be the same. The most preferred balanced reaction would be the reaction which have the lowest value of coefficients. Example would be the reaction of HCl and NaOH.

HCl + NaOH = NaCl + H2O (This would be the most preferred one since the coefficients are in the lowest value)
Other equivalents would be:

2HCl + 2NaOH = 2NaCl + 2H2O

3HCl + 3NaOH = 3NaCl + 3H2O

4HCl + 4NaOH = 4NaCl + 4H2O