The cache stores stuff from the sim as you fly, saves redownloading it if you load back into that same area. It’s possible (going off what FS2020 sometimes did) that old textures and objects with previous LOD models or textures, get stuck in the cache when there’s been an update, so if you delete the cache, it’ll just refresh it with a new one. Obviously, the drawback is, it’ll have to download the area you’re flying in again. But the upside is, at least it’ll be fresh new data. As I say, I’ve only noticed an extremely slight improvement.
3rd post down on this thread should help if you’re on MS Store version? Uninstall does not clear rolling cache
Also, once you do this be sure to to back into Online options in the sim to change the size of the cache back to your preference as it’ll default to 16gb.