The McRib is returning to menus this holiday season — but don’t get used to it.Related video above: Rossen Reports: Save money on fast food with these app tricksMcDonald’s announced Wednesday that its famed boneless pork patty sandwich will be available again starting Dec. 3. But, as always, it will only be for a limited time.And the same goes for another fan-favorite fast food item, Taco Bell’s Nacho Fries, which similarly hasn’t secured a permanent spot on the menu despite its popularity.Instead, limited offerings like the McRib or the Nacho Fries disappear and reappear with seemingly no pattern. Experts say that’s by design.Beyond boosting profits, highly anticipated seasonal products like the McRib create excitement among fans and an opportunity for companies to play around with promotions.On the other hand, a strategically timed rollout could also serve to generate positive news about the brand after bouts of bad press.“This is the …