Currently the user is still billed for shut down droplets because of the reserved resources. But on the other hand, when creating a snapshot and destroying the droplet, the IP can get lost.
I think it makes sense to offer a new mode where a snapshot is created and the droplet destroyed but the IP address(es) still reserved. This mode would then free up RAM, CPU and disk resources but keep the IP.
I think this mode could cost a reduced price like $ 0.001 per hour.