I was at FB from 2006-2015, and Scuba caused a phase change in how Facebook's performance was analyzed and how quickly insights were gained. For many of us in Infrastructure, we spoke of the pre-Scuba, post-Scuba eras. It was such a joy to have aggregated realtime performance metrics for our internet scale services and have the ability to drill down on just about any dimension when doing perf investigations. It gave us so much more confidence in our systems, both in our ability to detect issues, as well as pinpoint what was causing them.

I'd also like to echo what spicyj said about the UI, it is very usable. It was common for managers, PMs, and even people in completely non-technical business roles to use Scuba. It was my favorite internal product at FB and the one I miss the most.