Not really specific to this dual-chemistry though, the same holds true for normal EVs and for gasoline-powered cars.
Everyone already tried selling EVs with smaller batteries. The might be more efficient on paper but they don't sell. Turns out that trips people take once in a blue moon are still important to them, so a battery tuned to making that possible once in a blue moon sounds very useful.
A gallon of gas weighs around 6 pounds. A car usually has less than 20 gallon capacity. Keeping it half full would mean you keep 10 gallons which is 60 pounds. Even if you kept it full all the time, it is 120 pounds. That is going to be a lot less than any sizable battery ( theTesla Model 3 battery weighs around 1000 pounds).