Yev here -> Hah! It's less expensive and as long as failure rates are below a threshold for us - we will usually skew less expensive. Now, if failures start creeping up there's a lot more math involved, but since we're built for failure, we are very calm when a drive fails.

In some environments when a drive goes down, everyone goes into "red alert" mode and they have to rush to repair the drive or replace it. In our case we don't have to drop everything and run to it - so it helps keep the overall replacement costs down.