Lighting and physics are designed for the units scale, so you could potentially have some issues if you change the size, in particular if you scale things down then the physics will be less precise because the distance between steps would be greater.
You can use the World Composition tool to create large worlds without that issue though, it allows you to create the map in sections and will adjust the origin so that physics keep working. Just note that while the maximum size of a map is 20km x 20km the actual size that works OK with physics is around 6km x 6km