In a galvanic cell, the salt bridge does not participate chemically in the cell reaction. The salt bridge is a device used to provide electrical contact between the two solutions and therefore it completes the electrical circuit. In other words, it connects the oxidation and reduction half-cells of a galvanic cell. It maintains electrical neutrality in both the solutions by a flow of ions.
The ions of the electrolyte present in the salt bridge neither react with the ions of the electrode solutions, nor gets oxidized or reduced at the electrodes. In the absence of salt bridge, the solution in one-half would accumulate positive charge and the other half would accumulate negative charge, which will eventually result in preventing the reaction and thus electricity generation.
An electrochemical cell is a device that is used to create electrical energy through the chemical reactions which are involved in it. The electrical energy supplied to electrochemical cells is used to smooth the chemical reactions. In the electrochemical cell, the involved devices have the ability to convert the chemical energy to electrical energy or vice-versa.