Right, so...
1) The most annoying part of trading in the crypto space is typically the conversion between fiat and crypto. Depending on where you live that could be a taxable event, your bank could have a prob with it, bank transfers to and fro can take days (an eternity in the crypto trading world), etc.
2) The crypto market is almost entirely pegged to Bitcoin to some degree. Meaning, on a good day 1000 cryptos will increase in value, and on a bad day 1000 cryptos will decrease in value. What do you do when you want to day trade crypto, buy low and sell high?
3) Typically the crypto exchanges that trade the smaller market cap tokens don't accept fiat deposits at all. Their trading pairs are mainly between bitcoin and the altcoin in question (and more recently ethereum trading pairs have emerged)
Enter: Tether, aka USDT, aka Monopoly Money. It's pegged to the US Dollar, so when you're holding crypto and the market is up, you can move your holdings to Tether and retain your gains instead of losing your position when the entire crypto market downswings at the same time. And because it's not really the US Dollar, there aren't any regulations for it and crypto exchanges can trade it and utilize it freely.
The problem, of course, is that Tether is NOT ACTUALLY THE US DOLLAR. Allegedly Tether is backed 1:1 with USD as more Tether is "printed" and released into the market to support the volume of crypto trading occurring, but to my knowledge there's no real evidence of this being true. At any point this can and probably will all come crashing down, and awareness of just how sketchy and precarious the whole Tether situation is is finally being paid attention to in the general crypto space.