I know this is an old article, but I figured I'd give a reason why you should disable indexes.

Not all organizations have the ability to have dbs for applications and others for reporting. So, for EOM or EOY reporting, transactional indicies might cause these reports to take forever especially if there are rollups or aggregations. It's best practice to not have indexes that you don't need, but rather than drop and recreate for EOM or EOY reporting, you can disable. That way, the maintenance hit is not a constant.

Yes, I know.. This is not best practice period . But sometimes, the customer has their limitations.