Sometimes email is not the practical way to reach people. An event reminder, a service update, a change of plan, something that matters in the next two hours rather than the next two days.
Both run off the same audiences, so the question is only ever which one the moment deserves.
One system, one contact record. Open anything below and keep going from there.
The most useful group messages are relevant, timely and sent to people who expect to hear from you. Use text messaging responsibly, with appropriate recipient consent and opt-out practices.