Advantages of stopwatch given below:
Stop watches in general, are MORE accurate than regular wrist watches, since they can measure down to 1/100th of a second and even up to milliseconds.
In any race such as swimming or track a stop watch can provide split or lap times to determine an athlete’s performance during an event. By adjusting tempo and movement swimmers or runners can adjust their pace and breathing to insure they have enough energy in reserve for the end of a distance race.
Disadvantages of wristwatches given below:
Wristwatches are expensive than stopwatch. You can't go swimming with it on, they eventually die, you may become obsessive over the time, the constant ticking.