This file stores lightmap-related settings used for the last bake. These stored settings are only used in the case when post-processing is launched manually for reasons described in this post.
Anyway, the maximum size of the lightmap is a depracated setting in this file, because Shapespark now always bakes lightmaps of at most 4k x 4k size. Using larger size would cause a risk the scene would not work, because according to WebGL Stats ~30% of devices still does not support larger texture sizes.