More than 1TB a month. Just downloading one game from Steam can easily be more than 100GB these days. Downloading ML weights churns through gigabytes easily, as does downloading or streaming 4K movies.
What's the point of having gigabit download speed if you have to constantly worry about using up your cap? And paying an extra £5 for every 250GB extra seems like some arbitrary punishment for power users.
They don't pay for infrastructure based on bytes transferred so why should I as a customer pay this random made up number?