is it better to have uncompressed sim textures on or off in the settings? i don't really understand what it means.
For the best quality you want to turn uncompressed sim textures ON.
There are two sets of sim textures available in the game: one set is saved with compression to save file size, the other set is saved without compression and therefore has a larger file size.
Compression is good for slower computers that don’t have a lot of vram (vram is the amount of gb of ram your video card has), because textures use vram to load and it’s a finite resource. However, compression introduces what are known as artefacts into the texture. In practice this means they start to look lower quality, a little rough and blocky.
Uncompressed textures come without any of that compression, so they don’t have any artefacts and look exactly as they did when the maxis team created them. The downside is they are much larger in size, and therefore take up more vram to load.
TS4 was made with quite low end systems in mind because its players skew quite young and aren’t always typical gamers who play other demanding games, and so don’t always have great PCs. That’s why they offer a lot of lower quality settings, to help those people out so they can still play the game. But, even the high quality settings aren’t as demanding as a lot of other AAA games, for the same reason.
So turning on uncompressed sim textures should be quite doable for a good majority of people. Certainly, if you can run the game on higher settings you’ll be fine with them on. If you start to have performance problems, turning off uncompressed sim textures can be a good place to start because of the instant benefit to vram.