Thermometers are handy- but not necessary.
I like to glance at mine so I know where I am during a run-
it is helpful to have one in the boiler during heat up- so I know when I’m close to producing.
They are great for taking notes during a run- temp and proof etc…
but do you need one- nope- just keep a 5-8 drips a second and let her go
is it nice to have one? yes –