What advantages do altcoins have that differs it from bitcoin ?
The main advantage is that they are an alternative to BTC, they give a wide choice of different coins for each investor and user. Of course, this option of investment is more risky, but in the long term it has the potential much more if it is possible to choose suitable coins.
I see that black market transactions are still mostly used only BTC is the only payment method, I occasionally encounter some transactions that accept other methods such as Dash or Zcash. So in my opinion BTC is still more practical than the current altcoin