If you find yourself without a job offer, and are still interested in the company, writing a response can be a good idea.
Here is an example:
Thank you for meeting with me, I enjoyed learning more about the company and its future goals. Whilst naturally disappointed to discover that I have not been selected for the ........role, I am grateful for the opportunity to have engaged with your team.
I sincerely congratulate the successful candidate and wish them every success in their new role.
Should there be any developments concerning the position or if you perceive the potential for my skills and expertise to contribute elsewhere within your organisation, I would welcome the opportunity to discuss further.
Thank you once again for your time and consideration.