Dark_samurai is right. There are still problems with the lightmapper and even the radiosity image in the forecast shows some small leaking of light if you look at it very carefully.

This and some other unfinished features prevent artists from using A7. But scripters who are in love with Lite-C are happy with A7.

At the end you could ignore the lightmapper und use Ventilators plugin to add lightmaps to models. But you can also simply stick to A6.