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- REBUILDing indexes is almost never required. (Search this forum or "Ask Tom" for opinions.) So you probably don't want to do that either.
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I disagree with Tom when it comes for rebuilding indexes.
He suggested coalesce in stead of rebuilding indexes.
Many times when split block occurs, the index block gets splitted either 50/50 or 99/1 depending upon the incoming key value. So oracle adds another block in to the extents and old leaf block maintains a pointer to the new block. During the range scan this pointer mechanism helps oracle to traverse to the adjacent block. But physically this block need not necessarily be adjacent to the prev block in the disk. It could be anywhere in the disk.
Second, the empty blocks due to large number of deletion in the index are still maintained in the index tree stucture.

That is why in a large DSS/DW system, I usually drop and create indexes during the maintenance window to get best performance from the index.

Tamil