I think the highest risk we bare having them is the risk of them getting removed from the centralised exchange where it is traded or when they disconnect it from the original fiat, infact it's just using fiat digitally and that is even one thing we shouldn't try if we loved the idea of crypto. right now it seems that we are getting a lot of them more in use than it's even imagined. The fact that you can just get nuked out of your funds if they think it's bad money is one big risk we have made normal, their are evidence of them in the web and I believe that should be a lesson though.
That's why I think stablecoins are useful, but only when people clearly understand what kind of risk comes with them. Many users treat them like cash because the price stays close to fiat, but in reality you still depend on the company behind the token, the reserves they hold, and the platforms where you use it. If any of those parts fail, the stable value can quickly become a problem.
A lot of people only notice this during market stress, when withdrawals slows down or question about backing start appearing. So stablecoins are practical for transfers and short-term holding, but I personally wont treat them the same way as holding coins where you fully control the keys.