The theory goes like this: The Windows Registry grows as data is added to it, but it never shrinks when data is removed. A bloated and fragmented registry with a lot of empty space can slow down the boot time as well as performance. A Registry Defragmenter and Compactor will rebuild and re-index your registry to eliminate structural mistakes and corruption. But do you believe that a Registry Defragmenter/Compactor is safe to use and can bring about measurable improvement in start-up and performance? If so, which such tool do you use and recommend? Note: Please note that here I am NOT talking about Registry Cleaners, in which I do not believe. There are many threads on those anyway.