There's two parts to Chia: plotting and farming. Plotting is a one-time cost of ~5-10 hours for a SSD, and after that you can start farming and you continuously

There's two parts to Chia: plotting and farming. Plotting is a one-time cost of ~5-10 hours for a SSD, and after that you can start farming and you continuously earn Chia by proving your drive still contains the random data that got initialised during plotting. Erasing the drive would mean you have to start over and you lose ~10hrs of income.