After I delete entries in the registry using the registry cleaner does it compact the registry or just leave it as bloated as before with empty entries?
It doesn't compact the registry. One thing though is if you use Windows 10 there's really no reason to compact "defrag" the registry, it does it automatically by itself from what I've noticed when making full registry backups with the freeware program Tweaking.com - Registry Backup.
Example, install a bunch of Windows Updates and it can or will grow in size then within 1-2 weeks it shrinks down in size. Plus, Windows 10 registry should never be cleaned by registry cleaners (even Microsoft doesn't want anyone using them anymore) since all the updates make it an always moving target with things changing all the time that no registry cleaning tool could ever properly keep up with.