For me, sending a follow up email is not exclusive to meetings or interactions that end in action items and work product. An email that contains a simple thank you is quite powerful and goes a long way in building a lasting connection. It offers an additional touch point between two people, doubles the number of interactions between you and another individual, and adds to the foundation of the relationship. It offers feedback to the person and, at the very least, shows them you enjoyed meeting and appreciated their time.