How do you use gile[s] with Blitz3D?

It's a special tool. I mainly use it for lights creation and Rendering, as you said.

It is capable of smoothing round shapes, something most other lightmappers can't do. And it supports Global Illumination that can be used to get superrealistic Lights. Although, this should be added when all settings etc. are done and the final render is performed. It may by a little tricky to find a good configuration for real quick previews.