Why does the CCM "RebuildClosureTable" create more entries than it has deleted?

After my recent V.4.0.2 upgrade (from V.4.0.1) I decided to reindex everything and do also a rebuildClosureTable in CCM.

What makes me a bit nerveous is the fact, that the rebuildClosureTable has deleted lesser entries than it afterwards has created.

118366 existing closure table entries deleted.
54846 links processed.
121363 closure table entries created.

I know there was an issue with the Import of Workitem parent/child structures with help of the Eclipse Full Client, which should now be solved in V.4.0.2 (?). But I'm a bit unsure.

Questions:

• Could this be the reason for this difference?
• Do I correctly understand, if the system works perfect, the number of deleted entries should be equal to the number of created entries.
• What is not working correctly, if some entries are missing in the ClosureTable? I learned, some progress calculation will not be correct in plans. Are there other side effects?
• For what exactly is this ClosureTable? Why does the parent/Child relationship have to be stored in this table? This relationship is already in other tables stored.

Thanks for any light in this mystery.