Earlier quoted context omitted.
If Tether worked as it was advertised there would be no profit opportunity. The purported reason Tether exists is to help the crypto markets deal with the liquidity problems because of how difficult Fiat banking is, essentially Tethers value proposition was “we (by some miracle) have reliable banking, we can buy and sell 1 Tether for 1 USD at any time regardless of other crypto currencies value”. In reality Tether is…
You can invest the money, the same as banks do. It's why they don't charge you to store money with them, especially if your balance is high. You only need and should keep enough liquid cash needed to handle day to day withdrawals. Everything else is fair game up invest. See: https://en.m.wikipedia.org/wiki/Fractional-reserve_banking https://en.m.wikipedia.org/wiki/Bank_run
“[...] each tetherUSD in circulation represents one US dollar held in our reserves (i.e. a onetoone ratio) which means the system is fully reserved when the sum of all tethers in existence (at any point in time) is exactly equal to the balance of USD held in our reserve.”