This process re-creates DSpace's search and browse indices. Run it after anything you do to the install that could change the content of these indices (e.g. manually changing metadata, withdrawing items). In addition, run it if you decide to change your searchable metadata fields (see Modify search fields ).
You may wish to have a scheduled process (e.g.cron) to re-index DSpace daily. Lots of little changes that add up over time without a re-indexing can cause DSpace's search function to become erratic.