We feature flag just about every change we do for ease of implementation. It gets our code into production faster for us to test and makes for a smoother release thanks to our internal tools. When we're ready to ship, we just select what percentage to enable that feature flag for—1, 5, 10, 25, 50, 75, or 100%. Goal is to not make the site explode for our users :).

For a font change like this, that wasn't the major concern, but rolling it out incrementally did give me a safety blanket of sorts. In other changes, where we might overhaul a view or unveil a new feature, we want to make sure we don't trigger tons of exceptions inadvertently. A slower rollout means it's easier to respond to those things before they get out of hand.

Hope that helps!