Most computers can have hundreds, perhaps thousands of orphaned registry entries and still operate correctly and not have any performance issues related to the orphaned entries.
I have no knowledge of how a Registry works.
It is a fascinating, albeit a dry subject. Google it and read all you can. There are also many books on the subject. The basic recommendations are as follows:
1) Do NOT touch your registry without proper backups.
2) Don't touch with the registry if you are not having specific problems that can be corrected by altering the registry, and you have proper backups.
3) Don't touch your registry unless you know exactly what you are doing, or under the direction of someone who knows exactly what they are doing, and you have proper backups.
Deleting or changing the wrong entry can make your computer unbootable.