For the most part, the default configurations for SQL Server are pretty good. Yeah, there are a few you should definitely change (like say, the ones involving parallelism), but most of the others can be, uh, good enough as is.
But no one really likes “good enough,” right?
So most of us tweak some of these defaults to improve performance. Measure, adjust, document improvement, get a raise. Rinse repeat. And of course, if you’ve spend any time in SQL Server circles you’ll quickly learn one of the biggest improvements we can make for SQL Server isn’t even in SQL Server. It’s the Windows Power setting, which by default is set to “if you don’t need anything right now I’m gonna lay my processors down for a rest.”