Just as it is with hard drives, it is also recommended to sometimes defrag the Windows Registry. This will mean the information is more compact and accessible, but also will optimize it in general. It will fill in the empty spaces that obsolete entries have left behind.
Apart from defragging, Eusing Free Registry Defrag also checks and deletes invalid entries or those that don`t do anything but refer to an application that no longer exists.
Once all the non-essential information is deleted and the Registry defragged, you will get better efficiency, more space, quicker information access, better stability in Windows start-up, etc. Eusing Free Registry Defrag is totally free, but the authors ask for a donation if you like their program.