no, there isn't That said, SC2 supports various size textures and there is certain data that is unnecessary but sometimes still there.
2 prime examples are: Normal maps with more channels than needed having image data in them. If the Normal only uses 2 channels, then don't paste your image data is the others, its takes up space.
Smaller textures scaled up are often just fine. A 256x256 normal map is sometimes acceptable and is only a quarter the files size of a 1024x1024 normal.