A helmet light is massively useful when you do get a puncture in the middle of the night, needn't be a proper one, just a cheap head torch is ample enough.
But mainly as TSK said, great to read sign without jerking your bike toward it to glimpse it before veering away from the verge.
Bear in mind the law don't count helmets light as part of the bicycle if you intend to only ride with them.
A helmet light is massively useful when you do get a puncture in the middle of the night, needn't be a proper one, just a cheap head torch is ample enough.
But mainly as TSK said, great to read sign without jerking your bike toward it to glimpse it before veering away from the verge.
Bear in mind the law don't count helmets light as part of the bicycle if you intend to only ride with them.