I do this for a living. If you really wanna save yourself some money, depending on your plumbing(usually PVC, older houses might have cast iron), just put a bit of a cleaning agent and run hot water into your drain for 10-20 minutes weekly. The hot water alone every week will do more for your pipes in the long run.

If you’re doing this regularly you won’t have to run the water as long, maybe 5 minutes weekly. This helps to dissolve build up from stuff like grease and soap scum which catches other food debris and leads to clogs. Preventive maintenance is best, spend a little time and money now to save a lot of time and money later.

Mixing them together causes an exothermic reaction that releases a lot of CO2. Both the heat and the releasing of gas bubbles can also help to break up things. Also it’s unlikely that all will mix with all, so you get some pockets of basic and some pockets of alkaline, who knows what you’re trying to break up but some of either might help. The method they learned is kind of throwing everything at it cus something will work. You aren’t wrong, both methods have validity

Especially when it regurgitates back up in your other sink mixed with hair and grime