The burning of the flux creates a gas shield that protects the weld pool from oxygen intrusion. So does the Argon/CO2 mix. So you have two belt and suspender options:
1. Use both if either the flux or gas cloud is inadequate. This could be because it is a small job and you can’t justify getting another tank of the proper gas mix for your application. That’s OK, we understand. It might not be cheap for the hobbyist.
2. Get the right gas mix for the metals/wire/rod you are using so you don’t need the flux. Using flux is usually only necessary when you don’t have a proper inert gas (Argon mix) shield for the weld pool.
As a hobby welder, this stuff is often a trade-off and I still have a reel or two of fluxed wire-feed or torch rod, but I use it less and less. I always used a fluxed rod for stick welds (we had a Forney 250 amp stick welder) because it was old school and was open weld only.
I no longer do enough welding to be on a first name basis with my local welding resource supplier, so I don’t get deep discounts and let me tell yah, this stuff ain’t cheap, so I have my 80/20 Argon/CO2 bottle and that has to do for anything I MIG weld. Whether it works or not determines what I use for a wire or rod. I have a Clarke 130 MIG gas/no gas welder with a 50% duty cycle so it’s up to any challenge I throw at it, whether I am up to the challenge or not. Mostly, because it CAN run gas, I run no-flux wire and just use the gas, but I can’t tailor the gas mix to the metals being welded and used as wire filler so I just live with what I’ve got.
I make structurally strong MIG welds, not necessarily pretty MIG welds. You want pretty? Then I reach for the torch or TIG, especially for sheet metal welds. Or my angle grinder, after the fact.