Indexes? When should they be used?

When do we should not use the indexes?

In Inserts? In Updates? in Deletes?

If i have a massive delete like:

delete from table1 where column1='X' (2 million rows) should i have the index enabled or not?

Whats the best option? To disable indexes on massive inserts and then rebuild or to delete and recreate?

Best Regards

Luis,

You may find this thread useful.

My guess is that it may be more efficient to drop the indexes, do the action, and then rebuild the indexes. (However, that depends upon having either, 'down time' with little user activity, OR SQL 2005 Enterprise edition.