Personally, to me its not about functionality between 1.16 and 1.18.
It's about security and risk.
Running out outdated versions is a greater risk.
If you or your organization are willing to accept that risk then it would become about any new features/functionality.
That being said, you can view the release notes here:
https://github.com/osTicket/osTicket/releases
Then you investigate any new features, etc and try to determine if they are worth it to you / your organization.