SIGT! Low difficulty gives lots of coins

Lots of coins that aren't worth poop, But what do I know

With my older cards I am mining Zcash and with newer RX series i am mining Ether + Decred
They seem to be most stable in terms of return. Some coins give more but it is short lived
What new cards? & what's the advantage of mining both? I know lots do it but never quite understood the advantage. How is your Eth hashrate effected when you mine both?