Limited Liability. A limited liability company protects you from personal liability. A limited liability company does not protect businesses from legal liability. Multiple businesses under one LLC umbrella will not protect one business from legal claims against another business.
Example: You own three businesses: a restaurant, a rental property, and a printing business. All three businesses are under the same limited liability company, Frank's LLC. A slip and fall injury occurs at the restaurant. The resulting damages from the injuries are in excess of $500,000. Frank's LLC only has insurance for $250,000. The injured person could seek the remaining $250,000 from all three of Frank's LLC's businesses: the restaurant, the rental property, and the printing business. The outcome of a slip and fall injury at a restaurant is now having a detrimental impact on the other two businesses.
Licensing. A single LLC will need to file a DBA ("doing business as") for each business. You may also need special permitting for each business as well.