I do not see any use in stable coins, besides keeping the money on exchanges while searching for a market entry point. Besides, the most stable coins are regulated and are backed only by a certain percentage and not in full amount.
Besides that function, stable coins are also suitable for online payment instruments. At present we see a lot of shops that provide payment through crypto currencies that don't have a stable value, of course it has an impact if the network is slow. Prices change quickly but transaction speeds cannot match that.