trading the usd to your local currency, that's how you can see how it could affect lives of people around the world. if you wanted to buy BTC or any other crypto, you wanna to buy usdt using your local currency and then you can will realized how much you need to acquire 1USDT.
with the inflation today, one could argue if its the safest asset today. i certainly feel like there will be a runaway inflation by how US government handles it affairs.
if you mean how its price affects crypto trader, it don't affect much as its a stablecoin which tokens and BTC are priced in stablecoin.