It is loading them dynamically in the background constantly. If those textures are compressed, it’s doing work to load the compressed version into memory, CPU is reading it out of memory, decompressing it and putting it back in memory, then moving it to the GPU.

It will take 1.5x (assuming 50% reduction in the compressed copy, probably would be worse) the RAM plus the CPU overhead depending on compression algorithm.

That is happening while you’re playing.

Unless at load it is decompressing and storing the decompressed textures on your disk, in which case you need 1.5x (or more) of the original storage to play the game and compressing them in the first place is worse if the thing you’re optimizing for is game size on disk (which is what this thread is complaining about).