Over time the registry becomes larger and larger as new programs are
installed, used and removed. The design of the registry is such that when you
add some data into the registry it becomes larger, but when you remove this
data the registry will not shrink back to its previous size. Why? When a
registry entry is removed, that entry is simply marked as blank but remains
in place, introducing a gap into the registry. In this way the registry
becomes more and more fragmented over time.