I use NTregopt (freeware) and Winaso Regdefrag 1.2 (freeware) from time to time. Winaso is also showing the percentage of fragments.
With about 3,50 % fragments, and after that compacting you are saving
about 1,5 MB.
Sometimes I save *more* than 5- 7 MB!
More important however, that after compating the registry with Winaso
"your registry will acquire linear structure which will reduce application response time and registry access time." (!!)
With these arguments I think a compacting feature should be implemented in Powertools, otherwise it is like drinking wine from a beer glas .....