If ray depth setting is per material rather than general settings [calculated for the every pixel of the image] render time can be improved a lot. This is specially important for scene with lots of overlaping glasses/reflections. Though this kind of scene can be rendered twice, first the whole scene with a low ray depth and after only the glass region with a high ray depth. Anyhow will make more sense for ray depth to be per material.

Regards,

Iosif