One poor woman I worked with used to come in every day and kick off a bunch of queries that would do a couple linear scan of a database and take four-six hours to complete. I added a single one column index and the same query ran in less then a second. Got a hug on the spot. The DBA was upset the backup took a couple minutes longer to complete but when he complained he got into trouble for not profiling the queries and adding the index himself (ha!).
After that I started using SQLite for a lot of things - instead of confronting the DBAs I’d just dump the official database into an SQLite database and run all my queries against that. Was kind of amazing that you would have these huge Oracle clusters supporting a database with a few tens or hundreds of megabytes (not even gigabytes) of data but perfect size for slurping into SQLite on my desktop.