All considered, I suggest that you turn on the macOS firewall, and if you find things slowing down you can revisit the decision after some more research.
Leaving it off may be leaving you totally unprotected, and that's the worst situation you can be in.
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
