The price of USDT is always around $1.
Is USDT purposely controlled to be like that?
Yes, that's the aim. It is supposed to be a stable coin. There are several alternative stable coins now.
One good use for them is as a safe haven when the market turns bearish - if BTC or your favourite alt starts dropping in price, you can just convert to USDT to keep your money safe, and then convert back to BTC or alts once the prices start to recover. It's a simple way to increase your coins.
USDT is still crypto though, and does have a degree of risk attached. It doesn't always quite maintain the dollar peg, plus there always seems to be some new controversy about the coin. I'd post some links but you may as well just google 'ustd controversy'.
