Use Auto Display Intensity', is for when you use the "light" background and everything is white. It will dynamically adjust the brightness so that the screen is not so intense to look at e.g. when you open Outlook. Plus it saves battery life.
- 'Use Key Vibration Feedback' is for enabling/disabling the capacitive feedback on the three main buttons. We actually really like feedback, but we imagine there are a few who don't. Plus turning it of can help save a tiny bit of battery, we presume.
- Finally, 'Use Echo Cancellation' is for phone calls and basically does what it says--makes the audio more stable with less echo. We see no reason why we would want to disable it but it's nice it's there, we suppose.
While not groundbreaking settings, we do like the little extra control Sammy has given us. Unfortunately for the first setting, while it works well with the "light" theme, the Focus S still suffers from an over-zealous, power-conserving light sensor, making the phone more dim than we think it should be. To solve that, you can disable auto-brightness in Settings and leave on Medium (although that's a bit too bright sometimes).