It depends on a number of things, but mostly your application.

If your data is pretty volatile -- you have a huge number of update-inserts-deletes -- then it is sometimes worthwhile rebuilding indexes because they may become in-balanced.

However, unless you are seeing performance issues, or regularly delete-insert vast quantities of data I would say no, leave it alone.

So dont rebuild indexes unless you feel you have a problem. If you do have an issue and have to do this, then maybe make use of the 'alter index rebuild ' syntax to do it without interrupting service. Because remember - if you drop a primary index with users online, you run the risk of getting duplicates in the table.

Hope this helps.

Adam.