Hairballs are a common occurrence for most cats and generally aren't harmful when they happen occasionally. However, frequent hairball expulsion or unsuccessful gagging and retching without producing a hairball can indicate a problem. In such cases, a hairball may cause a blockage in the digestive tract, potentially leading to serious health issues like intestinal obstructions. These can require immediate veterinary attention. If left untreated, blockages could become life-threatening. Monitoring the frequency of hairballs and consulting a vet when patterns change is crucial for your cat's well-being.