I agree that timers are more useful, but from time to time there is a request in the HA community about a simple stopwatch.
You can see several use cases and requests in the community:
https://community.home-assistant.io/t/baby-sleep-stopwatch-timer/386170
https://community.home-assistant.io/t/garden-runners/188840
https://community.home-assistant.io/t/how-to-create-a-stopwatch-start-stop-via-wifi-button/121761
https://community.home-assistant.io/t/create-a-sensor-that-is-a-stopwatch-of-the-state-of-another-sensor/391066
https://community.home-assistant.io/t/stopwatch-helper/441079
https://community.home-assistant.io/t/creating-a-stopwatch-best-way-to-accomplish-this/348502
https://community.home-assistant.io/t/simple-stopwatch/306011
https://community.home-assistant.io/t/timer-and-stopwatch/188524