Xylitol kills strep bacteria and breaks down biofilms. It's a useful addition to toothpaste and sinus rinse to help breakdown plaque and prevent ear infections or throat infections by strep bacteria. It's also used in wound care formulations as a paste applied to a wound to help inhibit biofilm formation that slows healing.
Well, that might be. However, the Precautionary Principle applies here for me: saline and bicarb just mimic the chemistry inside your nose. Xylitol isn't necessary, so why introduce it? Who knows what side effects it might have?