No, but they are useful. Timers are used for brew processes that include a timed component... which is almost all of them! The most popular application for a timer will be with a pourover, where following the correct pour timings can be the difference between a cup of hot brown water and an amazing coffee. With a French press timing is important as well: you are steeping the grounds in the pot for about 4-5 minutes (too short and you won't get the maximum flavor extraction, too long and your coffee will get bitter). Timing is also used for Clever brewers and other less popular methods.