Yes, absolutely. IME, the worst fragmentation you get is at the leaf levels of a clustered index, and is the most necessary to rebuild. The higher levels of indexes generally don't get that badly fragmented, because there are fewer of them and more entries per page
As I mentioned, rebuild is functionally equivalent to DROP INDEX ... and CREATE INDEX ... (or CREATE INDEX ... WITH DROP_EXISTING)
If it only did the higher levels, then you'd have to do both a reorg and a rebuild to fully defrag an index, and that's a waste of typing. 🙂
Rebuild also updates the statistics on the index, something that reorg doesn't do.
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