Sell all ETH, BTC into Stable Coin when the market goes down
Your "advice" is quite normal and it is done by many people. Whenever the market goes down, it is advisable for you to store your BTC and alts to USDT for you to be safe. It is served as your "safe-haven."
USDT is the last shelter in this market and we can secure our assets when the market falls. I think keeping USDT when the market falls is an advantage because you will add a lot of new choices in investment and can buy any coin that is trending down but to do that you have to great patience and your decision will greatly affect your profit in the future