Basic idea is that on mobile we re-group the order of operations.

Before:
for (light in lights):
+ shadowpass(light)
+ lightpass(light)
+ volumepass(light)

After:
shadowpass(lights)
lightpass(lights)
volumepass(lights)

This could be a very common situation if your renderer was written for Desktop (IMR) and it has neglible effect there

But on some mobile platforms this may be a disaster, so you should watch out on order of things