Any bus compression should be treated with caution.
I have found anything even approaching -0.1db sounds horrible especially on the iPad - very compressed sounding. So I set a ceiling of -0.3db maximum. When I limit (using an L2) I initially set my track as high as possible with only about -2db headroom on the peaks, and when lowering the limiter I aim for -1db attenuation on the peaks at most. Otherwise...once again things will sound over-compressed on mobile devices.
Leaving small headroom in the dynamics is useful whenever you use lossy compression (aac, mp3, ogg etc) because of nature of that process. But the ingame volume should be set in the engine to make room for sound effects (if they are present). Other settings like limiting depends mostly on previous production stage - mixing of audio. There is notion towards not using limiters at all (or just to cut out short, single peaks) which seems resonable since we have so much controll over the whole process of music prodution today.