Oak Lucene Index - Reindex vs Rebuild

[nedk76542230]

1. What is the difference between re-indexing a Lucene index by setting the flag in CRXDE

Versus 

2. Forcing a rebuild of the index by deleting the index from the server and removing all the checkpints using

    java -jar oak-run-1.2.17.jar checkpoints crx-quickstart\repository\segmentstore rm-all

Does the reindexing do anything?  I was told by Adobe tech support that rebuilding the Lucene indexes was a recommended maintenance task.  Frequency as with many things based on each systems unique characteristics.

Thanks

 Ned