The answer is easy
If you convert your cryptocurrencies to fiat (like dollars or whatever), you may have to pay hefty fees trying to withdraw the fiat proceeds (and wait for days until you receive the funds). But with centralized stable coins, say tethers, you can completely bypass the fiat system (read, banks and all that pain in the ass that comes with them) and move your tethers either to your Tether account (or how it is called) or to another exchange where they are accepted. Essentially, these coins are working like fiat while without making use or having to use the banking system (under whatever name)
All right. The stable of the coin is precisely t thanks to which it is possible to quickly and with minimal fees fixed in a stable currency. However, the centralized side of these coins confuses me. It turns out that we, in the distance of cryptocurrencies, depend on two factors at once. The first is the project itself producing a stable coin, as Tezer knows, there are quite a few conflicts with the law that are still being resolved. The second factor is the exchange on which we speculate with this coin.