There are times to use a stop watch and times to leave it in your bag.
Competitive swimming is ultimately measured by time and this can become an obsession for all involved. As coaches we need to constantly remind ourselves that the results (race times) will be the best that they can be if we if we get the planning, training, technique and skills right. For the developing swimmer our focus needs to be targeting the above mentioned factors with only the occasional use of our stop watches in any given practice session.
When we need to be accurate with a time then use the stop watch but for most general training situations the pace clock will suitably provide.
Through the use of the pace clock swimmers learn to take responsibility and ownership of their training performances through personal monitoring of the times they are doing for repeats in the various training sets which have been designed for them.
The trap in over using a stop watch is that we spend our time watching the watch instead of watching our swimmers.
Stop watches can be used for areas other than timing specific swims. For example when your swimmers begin a set, start your stop watch. If the set is 20 x 50 on 60 seconds, you will know they have completed 20 repeats when the stop watch gets to 20 minutes. This can be a great way to give members of your swim team the responsibility to count repeats whilst you can quietly monitor how many they have done.
The stop watch is a great tool to measure stroke rate for older age group and open level swimmers. If your watch has the capability, change the mode to stroke rate and off you go. Each coach will measure the stroke rate at different times within each stroke. For example in freestyle, start the stop watch as the left hand finger tips enter the water and then let the swimmer do 3 complete stroke cycles (left and right arm) and stop the stop watch when left hand finger tips enter the water for the 3rd time. In butterfly, start the stop watch as the finger tips enter the water and then stop the stop watch as the finger tips enter on the 3rd stroke. The figure on the stop watch will show you how many strokes the swimmer would di in one minute at the same stroke rate they just swam.