Stable coins are coins tied to real currencies. Yes, this makes them more reliable and convenient to use, compared to other coins that now and then jump on exchanges like rabbits. But real money can also change its value depending on the economies of countries.Such coins are convenient for buying and selling other coins due to their stability in relation to other cryptocurrencies.
No. It doesn't make them more reliable or convenient. On the other hand, I would say that it makes them less trustworthy compared to other cryptocurrencies. In the case of stablecoins, some unknown individual or entity is holding the reserve funds and they issue tokens for these funds. If you own these tokens, then you don't directly own the reserve funds. It is very much possible that the individual or entity holding these funds will vanish without any warning, making the tokens completely useless.