The platform settings allow you to fine tune your region for each platform you want to publish to.
Space currently supports;
The default settings are designed to work for most regions.
Scene adjustment
Removing lightmaps and probes can significantly reduce download speed but will also impact on the runtime performance.
More information;
Lightmaps Light probes Reflection probes
Ticking these boxes will prebake data before export. This improves loading performance but the region download will be bigger.
More information;
Static bake meshes Static bake colliders
Occlusion data holds information about what areas are visible from other areas; it allows the viewer to make intelligent decisions about optimising a scene, however it can add several mb of size to both runtime memory use; and download size. Keeping it improves performance but can result in higher memory use in big scenes.
Navigation data is used for showing waypoints, and moving NPCs around in a scene; it uses a little bit of extra memory, and can be stripped out if you are under severe memory pressure.
Texture size reduction
All textures will be reduced to a maximum of the defined size for each build.
Reduces textures all by a multiple of the original, in line with Max texture reduction above.
So; if your scene contains large textures at 1024x1024 and you set the max texture reduction to 512 those large textures will be reduced by a factor of 4.
If you then set Texture reduction levels to 1, smaller textures in your scene will also be reduced by a factor of 4; so a 512x512 texture, which otherwise would have been unchanged by the Max texture reduction, would also be reduced by 4, to 256x256.
If you set the Texture reduction level to 2 it will multiply the Max texture reduction scale by 2; so in the case above reducing the smaller 512x512 texture by a factor of 8, to 64x64.
This will apply a further multiplicative reduction on normal maps on top of the reduction already applied by the Texture reduction level above.
Texture compression
Allows JPEG compression to be added to all textures in addition to DXT compression. This will degrade the quality of your images as the compression is lossy; but significantly reduces download filesize. It does not improve runtime memory size except during loading. Crunch level runs from 0 (very lossy) to 100 (lossless).
This applies a further quality reduction, comparable to the quality slider in Photoshop when saving a jpeg file.
Interprets images stored as 'True Color' to 16-bit colors. This applies compression to the colors, without introducing the blurriness / artefacts that DXT compression can introduce; at the expense of being slightly larger. With this ticked, any image with 'True Color' compression, will be packed at 16 instead of 32-bit on this platform.
Audio settings
Converts stereo files to mono for that platform.
This is a percentage field. So whatever the bitrate of your original files, you can reduce by X% for each of the different platforms you publish to. For instance a set of 128 bitrate original files, left at 100% in the Standalone build can be reduced to 64 in Mobile and WebGL builds by setting this field to 50.