You'll definitely have to use indexes if you want your database to perform but having too many indexes isn't good either. Save some storage and make your database faster by removing unnecessary indexes.
Finding a performance issue can be a tricky thing but if you know the tools available at Oracle, you'll sometimes even enjoy it. This article shows you how you can analyze a PL/SQL procedure or function.
You sure have a backup when running an Oracle database but sometimes it takes a while to restore a single table or even a single row. Oracle comes with a handy feature called "Flashback" which allows you to run a query on a table state from the past.
You're probably trying to avoid that but sometimes when you have to run a long running operation like a full table scan on a table with millions of rows, you'll want to know how long you have to wait until that operation finished. Check this article for more information.