Flux is used in very few spots.

1. You can buy things that boost void income.
2. You can run tempus fugit (on PC) to speedup the game by +50%, including Necrocorns These 2 are the main uses. once you buy Chronocontrol and Chronosurge it’s basically infinite, so you just run it all the time.
3. and later on fixing cryochambers, with fixing being always the same price, you can first buy several for cheap, and then fix the broken ones from before.