Probably not necessary to defrag the registry - but it is not the same as defragging the hard drive, so if you would feel better about doing it, I don't think it would hurt like doing a file system defrag. The registry files (hives) are pretty small compared to the size of the operating system. Let us know if it speeds things up
If you are using a specific tool, take a look at the support forums (if one exists) of the tool and ask them
there. Let us know if you find an answer you are satisfied with, as I am sure someone will ask this again.
Defragging the registry should be equivalent to writing a few MB to the disk, so it has no specific affect on your SSD. As to the value of doing this, like the other posters, I'm not sure.
I posted a similar question weeks ago and got all kinds of flack from the transistor heads, I use a program called Registry Mechanic and been using it for years . I contacted PC Tools the Mfg. And they said it was safe to defrag. the registry, just not the SSD.