If your catalytic converter is clogged then you will improve your gas mileage some by removing your catalytic converter.
Yes removing catalytic converter will improve your gas mileage some because a blocked or clogged catalytic converter creates back pressure on the engine which makes the engine use more fuel.
Just make sure you don't need to pass emission testing as in some places that have emission testing if you remove the catalytic converter then the car will fail the emission testing.
Some places require a catalytic converter to be installed or you'll fail the emission testing.
So check with your local laws and regulations as to whether or not you can remove the catalytic converter.
I removed my catalytic converters and doing so did give me a few miles per gallon increase in the fuel mileage.
I seem to have much more engine power as well.